Signalling in Coordinated Multi-Point Transmission and Reception (CoMP)

ABSTRACT

In a wireless communications system including a first base station and a second base station, a wireless communications method implemented in the first base station supporting coordinated multi-point transmission and reception (CoMP) is disclosed. The wireless communications method comprises receiving from the second base station an information element (IE) indicating multiple relative narrowband Tx (transmit) power (RNTP) thresholds, and performing interference aware scheduling. Other methods, systems, and apparatuses also are disclosed.

This application claims the benefit of

U.S. Provisional Application No. 62/055,381, entitled “Signalling for Inter-eNB CoMP,” filed on Sep. 25, 2014, U.S. Provisional Application No. 62/056,095, entitled “Signalling for Inter-eNB CoMP,” filed on Sep. 26, 2014, U.S. Provisional Application No. 62/076,221, entitled “CSI Exchange for Inter-eNB CoMP,” filed on Nov. 6, 2014, U.S. Provisional Application No. 62/076,873, entitled “CSI Exchange for Inter-eNB CoMP,” filed on Nov. 7, 2014, U.S. Provisional Application No. 62/110,006, entitled “CSI Exchange for Inter-eNB CoMP,” filed on Jan. 30, 2015, U.S. Provisional Application No. 62/145,251, entitled “Efficient CSI and e-RNTP Exchange for Inter-eNB CoMP,” filed on Apr. 9, 2015, U.S. Provisional Application No. 62/145,580, entitled “Efficient CSI and e-RNTP Exchange for Inter-eNB CoMP,” filed on Apr. 10, 2015, U.S. Provisional Application No. 62/150,178, entitled “CSI Exchange for Inter-eNB CoMP,” filed on Apr. 20, 2015, U.S. Provisional Application No. 62/151,796, entitled “Subband Definitions and eRNTP enhancements,” filed on Apr. 23, 2015, U.S. Provisional Application No. 62/161,804, entitled “On the Subband Definition in CSI Signaling,” filed on May 14, 2015, U.S. Provisional Application No. 62/162,285, entitled “eRNTP Signalling for Inter-eNB CoMP,” filed on May 15, 2015, U.S. Provisional Application No. 62/204,541, entitled “Subband definition in CSI Signaling,” filed on Aug. 13, 2015, the contents of all of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to coordinated multi-point transmission and reception (CoMP) in wireless or mobile communications and, more particularly, to signalling in inter-eNB (E-UTRAN NodeB or eNodeB) CoMP.

Referring now to FIG. 1, a CoMP mobile communications system 400 comprising a CoMP coordination zone or area or CoMP cooperating set 402 in which the embodiments may be implemented is illustrated. One or more user equipments (UEs) 410 are served by one or more TPs or cells 404 to 408. TPs 404 to 408 can be base stations or eNBs. Each of the user equipments includes e.g. a transmitter and a receiver, and each of the base stations or eNBs 104 includes e.g. a transmitter and a receiver.

Transmission layers are sometimes called “transmit layers” or “layers.” The number of transmission layers is known as “transmission rank” or “rank.” A codebook is a set of precoding matrices or precoders. A precoding matrix is also known as a codeword.

REFERENCE

-   [1] RP-141032, “New Work Item on Enhanced Signaling for Inter-eNB     CoMP,” June 2014. -   [2] R3-142582, “Way forward on WI: Enhanced signalling for inter-eNB     CoMP,” October 2014. -   [3] R1-141206, “Signaling Considerations for Inter-eNB CoMP”, NEC,     March 2014. -   [4] R3-151209, Change Request, May 2015.

BRIEF SUMMARY OF THE INVENTION

An objective of the present invention is to provide efficient channel state information (CSI) and/or relative narrowband Tx (transmit) power (RNTP) exchanges between eNBs.

An aspect of the present invention includes, in a wireless communications system including a first base station and a second base station, a wireless communications method implemented in the first base station supporting coordinated multi-point transmission and reception (CoMP). The wireless communications method comprises, for a given user equipment (UE) identification (ID) and a given channel state information (CSI) process, receiving from the second base station a plurality of CSI reports each of which comprises a rank indication (RI) and a channel quality indicator (CQI), wherein the second base station receives from one or more user equipments (UEs) RI and CQI information.

Another aspect of the present invention includes, in a wireless communications system including a first base station and a second base station, a wireless communications method implemented in the second base station supporting coordinated multi-point transmission and reception (CoMP). The wireless communications method comprises receiving from one or more user equipments (UEs) rank indication (RI) and channel quality indicator (CQI) information, and for a given user equipment (UE) identification (ID) and a given channel state information (CSI) process, transmitting to the first base station a plurality of CSI reports each of which comprises an RI and a CQI.

Still another aspect of the present invention includes a first base station supporting coordinated multi-point transmission and reception (CoMP) and used in a wireless communications system. The first base station comprises a receiver to receive from a second base station, for a given user equipment (UE) identification (ID) and a given channel state information (CSI) process, a plurality of CSI reports each of which comprises a rank indication (RI) and a channel quality indicator (CQI), wherein the second base station receives from one or more user equipments (UEs) RI and CQI information.

Still another aspect of the present invention includes a second base station supporting coordinated multi-point transmission and reception (CoMP) and used in a wireless communications system. The second base station comprises a receiver to receive from one or more user equipments (UEs) rank indication (RI) and channel quality indicator (CQI) information, and a transmitter to transmit to a first base station, for a given user equipment (UE) identification (ID) and a given channel state information (CSI) process, a plurality of CSI reports each of which comprises an RI and a CQI.

Still another aspect of the present invention includes a wireless communications method implemented in a wireless communications system supporting coordinated multi-point transmission and reception (CoMP) and including a first base station and a second base station. The wireless communications comprises transmitting from one or more user equipments (UEs) to the second base station rank indication (RI) and channel quality indicator (CQI) information, and for a given user equipment (UE) identification (ID) and a given channel state information (CSI) process, transmitting from the second base station to the first base station a plurality of CSI reports each of which comprises an RI and a CQI.

Still another aspect of the present invention includes a wireless communications system supporting coordinated multi-point transmission and reception (CoMP). The wireless communications system comprises a first base station, a second base station transmitting to the first base station, for a given user equipment (UE) identification (ID) and a given channel state information (CSI) process, a plurality of CSI reports each of which comprises a rank indication (RI) and a channel quality indicator (CQI), and one or more user equipments (UEs) transmitting to the second base station RI and CQI information.

An aspect of the present invention includes, in a wireless communications system including a first base station and a second base station, a wireless communications method implemented in the first base station supporting coordinated multi-point transmission and reception (CoMP). The wireless communications method comprises receiving from the second base station an information element (IE) indicating multiple relative narrowband Tx (transmit) power (RNTP) thresholds, and performing interference aware scheduling.

Another aspect of the present invention includes, in a wireless communications system including a first base station and a second base station, a wireless communications method implemented in the second base station supporting coordinated multi-point transmission and reception (CoMP). The wireless communications method comprises transmitting to the first base station an information element (IE) indicating multiple relative narrowband Tx (transmit) power (RNTP) thresholds, wherein the first base station performs interference aware scheduling.

Still another aspect of the present invention includes a first base station supporting coordinated multi-point transmission and reception (CoMP) and used in a wireless communications system. The first base station comprises a receiver to receive from the second base station an information element (IE) indicating multiple relative narrowband Tx (transmit) power (RNTP) thresholds, and a controller to perform interference aware scheduling.

Still another aspect of the present invention includes a second base station supporting coordinated multi-point transmission and reception (CoMP) and used in a wireless communications system. The second base station comprises a transmitter to transmit to the first base station an information element (IE) indicating multiple relative narrowband Tx (transmit) power (RNTP) thresholds, wherein the first base station performs interference aware scheduling.

Still another aspect of the present invention includes a wireless communications method implemented in a wireless communications system supporting coordinated multi-point transmission and reception (CoMP) and including a first base station and a second base station. The wireless communications comprises transmitting from the second base station to the first base station an information element (IE) indicating multiple relative narrowband Tx (transmit) power (RNTP) thresholds, and performing at the first base station interference aware scheduling.

Still another aspect of the present invention includes a wireless communications system supporting coordinated multi-point transmission and reception (CoMP). The wireless communications system comprises a first base station, and a second base station transmitting to the first base station an information element (IE) indicating multiple relative narrowband Tx (transmit) power (RNTP) thresholds, wherein the first base station performs interference aware scheduling.

An aspect of the present invention includes, in a wireless communications system including a first base station and a second base station, a wireless communications method implemented in the first base station supporting coordinated multi-point transmission and reception (CoMP). The wireless communications method comprises receiving, from the second base station, a user equipment (UE) identification (ID) for a UE in a reference signal received power (RSRP) report, and using the UE ID to link the RSRP report with another measurement result for the UE.

Another aspect of the present invention includes, in a wireless communications system including a first base station and a second base station, a wireless communications method implemented in the second base station supporting coordinated multi-point transmission and reception (CoMP). The wireless communications method comprises transmitting, to the first base station, a user equipment (UE) identification (ID) for a UE in a reference signal received power (RSRP) report, wherein the first base station uses the UE ID to link the RSRP report with another measurement result for the UE.

Still another aspect of the present invention includes a first base station supporting coordinated multi-point transmission and reception (CoMP) and used in a wireless communications system. The first base station comprises a receiver to receive, from the second base station, a user equipment (UE) identification (ID) for a UE in a reference signal received power (RSRP) report, and a controller to use the UE ID to link the RSRP report with another measurement result for the UE.

Still another aspect of the present invention includes a second base station supporting coordinated multi-point transmission and reception (CoMP) and used in a wireless communications system. The second base station comprises a transmitter to transmit to the first base station, a user equipment (UE) identification (ID) for a UE in a reference signal received power (RSRP) report, wherein the first base station uses the UE ID to link the RSRP report with another measurement result for the UE.

Still another aspect of the present invention includes a wireless communications method implemented in a wireless communications system supporting coordinated multi-point transmission and reception (CoMP) and including a first base station and a second base station. The wireless communications comprises transmitting, from the second base station to the first base station, a user equipment (UE) identification (ID) for a UE in a reference signal received power (RSRP) report, and using at the first base station the UE ID to link the RSRP report with another measurement result for the UE.

Still another aspect of the present invention includes a wireless communications system supporting coordinated multi-point transmission and reception (CoMP). The wireless communications system comprises a first base station, and a second base station transmitting to the first base station, a user equipment (UE) identification (ID) for a UE in a reference signal received power (RSRP) report, wherein the first base station uses the UE ID to link the RSRP report with another measurement result for the UE.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a block diagram of a CoMP system.

DETAILED DESCRIPTION Embodiment A A1. Introduction

In the following we provide our views on channel state information (CSI) and enhanced relative narrowband Tx (transmit) power (eRNTP) exchange as well as proposals containing the required message structure.

A2. Discussion

A2.1 CSI Exchange

One eNB can send CSI report pertaining to one or more of its users to a neighboring eNB.

For each UE the CSI that the eNB sends can comprise:

CQI (channel quality indication): up-to 2 CQIs, each including a wideband CQI or component and possible sub-band differential CQIs or components

RI: wideband component

We note that the PMI was excluded from the CSI exchange report. The justification for this exclusion was to minimize the overhead and the fact that PMI can depend on fast changing channel information, thus reducing its utility over non ideal backhaul with a higher latency. However, in the absence of PMI the use of RI is limited. Indeed, any rank greater than 1 will convey only 2 CQIs, one for each of the two codewords. No further information about the (average) spatial directions seen by that user can be deduced by the eNB receiving the report. As a result, reporting the RI should be made optional. Moreover, the eNB requesting the CSI report should be able to able to specify whether or not it would like to receive RI reports. This can be achieved by setting a bit (for instance in the CSI Measurement Report type field) to be 0 if rank is not requested and 1 otherwise. Similarly, the eNB requesting the CSI reports should be able to specify whether or not it requires subband specific CQI reports. Another bit can be set to 0 if subband CQIs are not requested and 1 otherwise. The response of the eNB receiving the request can be mandated to comply with this request, i.e., that eNB can decide to include a rank indication in its response only if it is requested in the CSI measurement report type field of the corresponding request. Further, the subband specific CQI can be included only if they are requested in the CSI measurement report type field of the corresponding request.

In this context, we note that a CSI process can be defined to be the reference process for another one. In that case the latter process will reuse the rank determined for its reference process. It can be beneficial to exploit reference rank in the X2 signalling as well. One way to achieve this is to include another bit in the CSI Measurement Report type field which specifies whether or not a single rank is requested. In particular, this bit can be set to 1 only if the rank request bit is also set to 1. In that case the eNB receiving the request should understand that the requesting eNB is requesting CSI reports where only one rank is reported for each user. The response of the eNB receiving the request can be mandated to comply with this request, i.e., if the eNB decides to include a rank indication in its response then it has to be one indication per user.

Alternatively, no such mandate can be enforced, in which case it is up-to the eNB whether or not to include a rank indication in the CSI corresponding to each CSI-process of each user and the ranks indicated for a particular user need not be identical.

One of the goals of CSI exchange was to facilitate centralized RRM. In a scenario with centralized RRM, the central node receiving the CSI reports should be able to keep track of the CSI information received for each particular UE, over all the received CSI reports. This can be achieved by including a UE identifier in each CSI report for each UE whose CSI is conveyed in that report.

Moreover, for each CSI in the report, the CSI process configuration information should be included in order to convey the conditions under which the CSI was measured by the UE. This configuration information includes non-zero power CSI-RS information and IMR information (including, for example, the subframe indices and zero-power CSI-RS information). Since this configuration is anyway informed to the UE via higher layer signaling, for instance CSI-RS in tables 7.2.6 of TS36.213, and tables 6.10.5.2-1, 6.10.5.2-2 of TS36.211 and subframe indices in tables 7.2.6 of TS36.213, and table 6.10.5.3-1 of TS36.211, the same signaling can be reused to convey the configuration to the neighboring eNB. Another way of conveying this configuration information is through a look-up-table. A look-up-table mapping an index to each distinct applied CSI process configuration can be constructed for each eNB. Here, by an applied CSI process we mean a process that is used by at-least one served UE to measure its CSI. Such a table can be conveyed beforehand by it to eNB1, and then each report can include an index which will inform. Such a table can also be exchanged among neighbor eNBs first, and then the configuration information can be exchanged via indices.

We note that the period specified in the request by eNB1 to a neighboring eNB2 (via the Reporting Periodicity of CSI Measurement Report field) can be different from the periodicity with which the CSI is measured by a UE as per a CSI process, and then reported (over the air) to eNB2. To address such scenarios, eNB2 can either subsample (for example select the most recently received CSI) or average (over all CSIs received after those considered while determining the previous response) and send its response to eNB1, for example, about the CSI process configuration information. Note that the averaging can be done over the CQIs for a given codeword, given rank and given subband. The most recent received rank can be used for averaging.

A2.2 eRNTP Exchange

Our view on eRNTP exchange is captured in a corresponding proposal.

We note that the RNTP for the first subframe is always conveyed. If no information about the downlink (DL) power restriction on any subsequent subframe is conveyed, then the one conveyed for the first subframe can be assumed to remain static (i.e., applicable over subsequent subframes).

A3. Conclusion

We discussed the necessary X2 message to support CSI and eRNTP exchange for inter-eNB CoMP and presented corresponding proposals.

Proposals

9.1.2.1 LOAD INFORMATION

This message is sent by an eNB to neighbouring eNBs to transfer load and interference co-ordination information.

Direction: eNB₁→eNB₂.

TABLE A1 IE type IE/Group and Semantics Assigned Name Presence Range reference description Criticality Criticality Message Type M 9.2.13 YES ignore Cell Information M YES ignore >Cell Information 1 . . . EACH ignore Item <maxCellineNB> >>Cell ID M ECGI Id of the — — 9.2.14 source cell >>UL O 9.2.17 — — Interference Overload Indication >>UL High 0 . . . — — Interference <maxCellineNB> Information >>>Target Cell M ECGI Id of the cell — — ID 9.2.14 for which the HII is meant >>>UL High M 9.2.18 — — Interference Indication >>Relative O 9.2.19 — — Narrowband Tx Power (RNTP) >>ABS O 9.2.54 YES ignore Information >>lnvoke O 9.2.55 YES ignore Indication >>Intended O ENUMERATED One of the YES ignore UL-DL (sa0, sa1, UL-DL Configuration sa2, sa3, configurations sa4, sa5, defined in sa6, . . .) TS 36.211 [10]. The UL subframe(s) in the indicated configuration is subset of those in SIB1 UL-DL configuration. This IE applies to TDD only. >>Extended UL O 9.2.67 This IE YES ignore Interference applies to Overload Info TDD only. >>Enhanced O 9.2.x2 YES ignore Relative Narrowband Tx Power (eRNTP) Range bound Explanation maxCellineNB Maximum no. cells that can be served by an eNB. Value is 256.

9.1.2.11 RESOURCE STATUS REQUEST

This message is sent by an eNB₁ to a neighbouring eNB₂ to initiate the requested measurement according to the parameters given in the message.

Direction: eNB₁→eNB₂.

TABLE A2 IE type IE/Group and Semantics Assigned Name Presence Range reference description Criticality Criticality Message Type M 9.2.13 YES reject eNB1 Measurement M INTEGER Allocated by eNB₁ YES reject ID (1 . . . 4095, . . .) eNB2 Measurement C- INTEGER Allocated by eNB₂ YES ignore ID ifRegistrationRequestStop (1 . . . 4095, . . .) Registration M ENUMERATED A value set to YES reject Request (start, stop, . . .) “stop”, indicates a request to stop all cells measurements. Report O BITSTRING Each position in YES reject Characteristics (SIZE(32)) the bitmap indicates measurement object the eNB₂ is requested to report. First Bit = PRB Periodic, Second Bit = TNL load Ind Periodic, Third Bit = HW Load Ind Periodic, Fourth Bit = Composite Available Capacity Periodic, this bit should be set to 1 if at least one of the First, Second or Third bits is set to 1, Fifth Bit = ABS Status Periodic, Xth Bit = UE-CSI Periodic. Other bits shall be ignored by the eNB₂. Cell To Report 1 Cell ID list for YES ignore which measurement is needed >Cell To Report 1 . . . EACH ignore Item <maxCellineNB> >>Cell ID M ECGI — — 9.2.14 Reporting Periodicity O ENUMERATED YES ignore (1000 ms, 2000 ms, 5000 ms, 10000 ms, . . .) Partial Success O ENUMERATED Included if partial YES ignore Indicator (partial success is allowed success allowed, . . .) CSI Measurement O BITSTRING Each position in YES ignore Report type (SIZE(2)) the bitmap indicates the type of CSI measurement to report. First bit = Rank, Second bit = subband CQI. Reporting Periodicity O ENUMERATED Periodicity for CSI YES ignore of CSI Measurement (5 ms, 10 ms, Measurement Report 20 ms, 40 ms, Report Periodic 80 ms, aperiodic, . . .) Range bound Explanation maxCellineNB Maximum no. cells that can be served by an eNB. Value is 256. Condition Explanation ifRegistrationRequestStop This IE shall be present if the Registration Request IE is set to the value “stop”.

9.1.2.14 RESOURCE STATUS UPDATE

This message is sent by eNB₂ to neighbouring eNB₁ to report the results of the requested measurements.

Direction: eNB₂→eNB₁.

TABLE A3 IE type IE/Group and Semantics Assigned Name Presence Range reference description Criticality Criticality Message Type M 9.2.13 YES ignore eNB1 M INTEGER Allocated by YES reject Measurement ID (1 . . . 4095, . . .) eNB₁ eNB2 M INTEGER Allocated by YES reject Measurement ID (1 . . . 4095, . . .) eNB₂ Cell Measurement 1 YES ignore Result >Cell 1 . . . EACH ignore Measurement <maxCellineNB> Result Item >>Cell ID M ECGI 9.2.14 >>Hardware O 9.2.34 Load Indicator >>S1 TNL Load O 9.2.35 Indicator >>Radio O 9.2.37 Resource Status >>Composite O 9.2.44 YES ignore Available Capacity Group >>ABS Status O 9.2.58 YES ignore >> UE-CSI O 9.2.x1 YES ignore Report Range bound Explanation maxCellineNB Maximum no. cells that can be served by an eNB. Value is 256.

9.2.x1 UE-CSI Report

This information element (IE) provides UE-CSI information for a subset or set of UEs served by eNB₂.

TABLE A4 IE type and IE/Group Name Presence Range reference Semantics description UE subset CSI Report 1 . . . <maxUEsubsetCSIReport> >C-RNTI M BIT STRING ID of the UE served by (SIZE (16)) the cell in eNB₂. Defined in TS 36.331. >UE-CSI process 1 . . . information <maxUE-CSIprocess> >>Rank Indicator O INTEGER The rank indicator is (1 . . . 8, . . . ) present only if it is or BIT STRING requested in the (SIZE (3)) associated request. Cf. TS 36.213 [7.2.3]. >>Wideband CQI For M INTEGER Cf. TS 36.213 [7.2.3]. Codeword 0 (0 . . . 15, . . . ) or BIT STRING (SIZE (4)) >>Wideband CQI For O INTEGER Cf. TS 36.213 [7.2.3]. Codeword 1 (0 . . . 15, . . . ) or BIT STRING (SIZE (4)) >>Subband CQI For 0 . . . 0 indicates no subband Codeword 0 List or <maxCQISubbands > CQI, which is always Subband CQI List chosen if associated request does not want subband CQI >>>Subband CQI for O INTEGER Cf. TS 36.213 [7.2.3]. codeword 0 (0 . . . 15, . . . ) or BIT STRING (SIZE (2)) >>>Subband CQI for O INTEGER Cf. TS 36.213 [7.2.3]. codeword 1 (0 . . . 15, . . . ) or BIT STRING (SIZE (2)) >>UE-CSI process M INTEGER CSI process Configuration information (0 . . . 31) configuration or FFS information. Range bound Explanation maxUEsubsetCSIReport Maximum UE subset size for which UE-CSI can be reported. The value is 32. maxUE-CSIProcess Maximum number of CSI processes per-UE. The value is 4. maxCQISubbands Maximum number of subbands for UE CQI reporting. The value is 28.

maxUEsubsetCSIReport can alternatively be set to 16, 20, 30, 35, or 40.

9.2.x2 Enhanced Relative Narrowband Tx Power (E-RNTP)

This IE (information element) provides an indication on DL power restriction per PRB (physical resource block) per subframe in a cell and other information needed by to a neighbour eNB for interference aware scheduling.

TABLE A5 IE/Group IE type and Semantics Assigned Name Presence Range reference description Criticality Criticality RNTP Per M BIT Each position — — PRB STRING in the bitmap (6 . . . 110, . . .) represents a n_(PRB) value (i.e. first bit = PRB 0 and so on), for which the bit value represents RNTP (n_(PRB)), defined in TS 36.213 [11]. Value 0 indicates “Tx not exceeding RNTP threshold”. Value 1 indicates “no promise on the Tx power is given”. This IE is used to indicate DL power restriction per PRB for the first subframe. In case the DL power restriction is static, the indicated DL power restriction is maintained over the subsequent subframes. RNTP M ENUMERATED RNTP_(threshold) — — Threshold (−∞, −11, is defined in −10, −9, −8, TS 36.213 −7, −6, −5, −4, [11]. −3, −2, −1, 0, 1, 2, 3, . . .) Number Of M ENUMERATED P (number of — — Cell-specific (1, 2, 4, . . .) antenna ports Antenna for Ports cell-specific reference signals) defined in TS 36.211 [10] P_B M INTEGER P_(B) is defined — — (0 . . . 3, . . .) in TS 36.213 [11]. PDCCH M INTEGER Measured by — — Interference (0 . . . 4, . . .) Predicted Impact Number Of Occupied PDCCH OFDM Symbols (see TS 36.211 [10]). Value 0 means “no prediction is available”. Starting M INTEGER Number of SFN (0 . . . 1023, . . .) the first system frame from which the RNTP Per PRB Per Subframe IE is valid. Starting M INTEGER Index of the Subframe (0 . . . 9, . . .) first subframe Index from which the RNTP Per PRB Per Subframe IE is valid. RNTP List O 2 . . . The first item <maxnoofSubframes> in the list corresponds to the second subframe, the second to the third subframe, and so on. The DL power restrictions conveyed for the first subframe and the ones conveyed for the subsequent subframes in the list, are together applied repeatedly. >RNTP M BIT STRING Each position Per PRB (6 . . . 110, . . .) in the bitmap Subframe- represents a Specific n_(PRB) value (i.e. first bit = PRB 0 and so on), for which the bit value represents RNTP (n_(PRB)), defined in TS 36.213 [11]. Value 0 indicates “Tx not exceeding RNTP threshold”. Value 1 indicates “no promise on the Tx power is given”. This IE is used to indicate DL power restriction per PRB for the corresponding subframe. Range bound Explanation maxSubframe Maximum number of subframes. Value is 40.

Embodiment B B1. Introduction

In the following we provide our views on CSI and eRNTP exchange, as well as proposals containing the required message structures.

B2. Discussion

B2.1 CSI Exchange: Configuring CSI Processes

The concept of CSI processes was defined in Rel.11 to enable CSI feedback from a UE to its serving eNB. The CSI feedback is determined for each CSI process according to the serving TP and interference hypothesis configured in that process. Each CSI process that is configured for a UE, comprises a set of resource elements on which non-zero power CSI-RSs are sent and a channel estimate is obtained by that UE using observations received on those resource elements.

In addition, a set of resource elements is also indicated by the CSI process (referred to as interference measurement resources (IMRs)) on which the UE estimates the covariance of the interference it observes. The channel and covariance estimates are together used by the UE to determine and send its feedback report corresponding to that CSI process. Multiple such CSI processes (up-to 4) can be configured for a UE, each process corresponding to a different choice of signal or interference hypothesis. Moreover, in the scenario in which fast switching of the serving TP is not possible, different CSI processes that are configured for any given UE typically correspond to different choices of interference hypothesis.

Note from the brief discussion above that in the event the interference hypothesis of a configured CSI process presumes muting from a TP (that is a dominant interferer for the UE of interest) which is controlled by the neighboring eNB, coordination among the eNBs is required in order to ensure that the interference estimated by the UE on the constituent IMRs is consistent with the assumed hypothesis. Another similar event that requires coordination is if the non-zero power CSI-RSs indicated in the CSI process must be interference protected in order to ensure reliable channel estimation at the UE. In both these events, the dominant interferer that is controlled by the neighboring eNB must be muted on certain resource elements. Thus, a mechanism (with appropriate signaling) should be available to share the CSI-RS (comprising non-zero power CSI-RSs and IMRs) configurations between eNBs, which would facilitate configuration of CSI processes across multiple eNBs.

Once the CSI processes are configured, the CSI exchanged among eNBs over the backhaul should include the respective CSI process configuration information, in order to convey the conditions under which the CSI was measured by the UE. This configuration information includes non-zero power CSI-RS information and IMR information (comprising the subframe indices and zero-power CSI-RS information). Since this configuration is anyway informed to the UE via RRC (or higher layer) signaling, the same information can be reused as a container to convey the configuration to the neighboring eNB.

Another way of conveying this configuration information is through a look-up-table. A look-up-table mapping an index to one or more distinct applied CSI process configurations can be constructed for each eNB. Here, by an applied CSI process we mean a process that is used by at-least one UE served by that eNB to measure its CSI. Such a table can be exchanged among neighbors first and from then on the configuration information can be exchanged via indices. The total number of configurations in the table can be limited in order to limit signaling overhead.

Suitable values for the number of configurations in this table are either 8 or 16 or 32.

B2.2 CSI Exchange: Contents

One eNB can send CSI report pertaining to one or more of UEs to a neighboring eNB. For each UE, the CSI that the eNB sends to a neighbor can comprise:

(i) CQI: up-to 2 CQIs, each including a wideband component and possible sub-band differential components

(ii) RI (rank indicator): one wideband component

We note that the PMI was excluded from the CSI exchange report [1]. The justification for this exclusion was to minimize the overhead and the fact that PMI can depend on fast changing channel information, thus reducing its utility over non ideal backhaul with a higher latency. However, in the absence of PMI the use of RI is limited. Indeed, any rank greater than 1 will convey only 2 CQI(s), one for each of the two codewords. No further information about the (average) spatial directions seen by that UE can be deduced by the eNB receiving the report. As a result, reporting the RI should be made optional. Moreover, the eNB requesting the CSI report should be able to specify whether or not it would like to receive RI reports. Similarly, the eNB requesting the CSI reports should be able to specify whether or not it requires subband specific CQI reports. This can be achieved by setting a bit (in the measurement request) to be 0 if rank is not requested and 1 otherwise. Another bit can be set to 0 if subband CQIs are not requested and 1 otherwise.

Processing (filtering or subsampling) of the short-term CSI (received via over-the-air signaling) at an eNB prior to exchange should be permitted.

One use case for this is when the periodicity of the CSI report that is requested by eNB1 to its neighbor eNB2, is larger than the over-the-air CSI signaling periodicity configured by eNB2. In this case eNB2 has to do some processing (such as subsampling or averaging) of the reports it receives before it sends it to eNB1. In this context, we note that the subsampling employed by eNB2 should be understood by eNB1 (if needed additional signaling can be added to ensure this). One possible way this can be accomplished (without any signaling overhead) is for eNB2 to use the subsampling factor determined by a pre-determined rule (known to or configured for all eNBs in advance) that outputs a subsampling factor, given the requested periodicity and CSI process configuration as inputs. On the other hand, averaging or scaling or filtering employed by eNB2 can be transparent to the receiving eNB1.

One of the goals of CSI exchange is to facilitate centralized RRM [3]. In a scenario with centralized RRM, the central node receiving the CSI reports should be able to keep track of the CSI information received for each particular UE, over all the received CSI reports. This can be achieved by including a UE identifier in each CSI report for each UE whose CSI is conveyed in that report. We want to include a unique ID (identification or identifier) for each user so that the receiving node knows which ones among all the reports that it receives, belong that user. This will be useful for RRM. Otherwise the receiving eNB will regard each received report as belonging to a distinct user. This can lead to sub-optimal resource allocation.

B2.3 eRNTP Exchange

Our view on eRNTP exchange is captured in a corresponding proposal attached in the end of this embodiment.

We note that the RNTP (i.e., downlink (DL) power restriction) for the first subframe is always conveyed. If no information about the DL power restriction on any subsequent subframe is conveyed, then the one conveyed for the first subframe can be assumed to remain static (i.e., applicable over subsequent subframes).

We also present several variations, one of which includes the use of multiple thresholds

B3. Conclusion

We discussed the necessary X2 message to support CSI and eRNTP exchange for inter-eNB CoMP and presented corresponding proposals.

Proposals

9.1.2.11 RESOURCE STATUS REQUEST

This message is sent by an eNB₁ to a neighbouring eNB₂ to initiate the requested measurement according to the parameters given in the message.

Direction: eNB₁→eNB₂.

TABLE B1 IE type and Semantics Assigned IE/Group Name Presence Range reference description Criticality Criticality Message Type M 9.2.13 YES reject eNB1 M INTEGER Allocated by YES reject Measurement ID (1 . . . 4095, . . . ) eNB₁ eNB2 C-ifRegistrationRequestStop INTEGER Allocated by YES ignore Measurement ID (1 . . . 4095, . . . ) eNB₂ Registration M ENUMERATED A value set to YES reject Request (start, “stop”, stop, . . . ) indicates a request to stop all cells measurements. Report O BITSTRING Each position YES reject Characteristics (SIZE(32)) in the bitmap indicates measurement object the eNB₂ is requested to report. First Bit = PRB Periodic, Second Bit = TNL load Ind Periodic, Third Bit = HW Load Ind Periodic, Fourth Bit = Composite Available Capacity Periodic, this bit should be set to 1 if at least one of the First, Second or Third bits is set to 1, Fifth Bit = ABS Status Periodic, Xth Bit = UE-CSI Periodic. Other bits shall be ignored by the eNB₂. Cell To Report 1 Cell ID list for YES ignore which measurement is needed >Cell To 1 . . . <maxCellineNB> EACH ignore Report Item >>Cell ID M ECGI — — 9.2.14 Reporting O ENUMERATED YES ignore Periodicity (1000 ms, 2000 ms, 5000 ms, 10000 ms, . . . ) Partial Success O ENUMERATED Included if YES ignore Indicator (partial partial success success is allowed, . . . ) allowed CSI O BITSTRING Each position YES ignore Measurement (SIZE(2)) in the bitmap Report type indicates the type of CSI measurement to report. First bit = Rank, Second bit = subband CQI. ((Reporting O ENUMERATED Periodicity YES ignore Periodicity of CSI (5 ms, for CSI Measurement 10 ms, Measurement Report 20 ms, 40 ms, Report 80 ms, Periodic aperiodic, . . . ) Explanation Range bound maxCellineNB Maximum no. cells that can be served by an eNB. Value is 256. Condition ifRegistrationRequestStop This IE shall be present if the Registration Request IE is set to the value “stop”.

9.1.2.14 RESOURCE STATUS UPDATE

This message is sent by eNB2 to neighbouring eNB1 to report the results of the requested measurements.

Direction: eNB₂→eNB₁.

TABLE B2 IE type and Semantics Assigned IE/Group Name Presence Range reference description Criticality Criticality Message Type M 9.2.13 YES ignore eNB1 M INTEGER Allocated by YES reject Measurement ID (1 . . . 4095, . . . ) eNB₁ eNB2 M INTEGER Allocated by YES reject Measurement ID (1 . . . 4095, . . . ) eNB₂ Cell 1 YES ignore Measurement Result >Cell 1 . . . <maxCelline NB> EACH ignore Measurement Result Item >>Cell ID M ECGI 9.2.14 >>Hardware O 9.2.34 Load Indicator >>S1 TNL O 9.2.35 Load Indicator >>Radio O 9.2.37 Resource Status >>Composite O 9.2.44 YES ignore Available Capacity Group >>ABS Status O 9.2.58 YES ignore >> UE-CSI O 9.2.x1 YES ignore Report Range bound Explanation maxCellineNB Maximum no. cells that can be served by an eNB. Value is 256.

9.2.x1 UE-CSI Report

This IE provides UE-CSI information for a set of UEs served by eNB₂.

TABLE B3 IE type and Semantics IE/Group Name Presence Range reference description UE subset CSI 1 . . . Report <maxUEsubsetCSIReport > >(C-RNTI) UE ID M BIT STRING (SIZE ID of the UE served by (16)) the cell in eNB₂. Defined in TS 36.331. >UE-CSI process 1 . . . information <maxUE-CSI process> >>Rank O BIT STRING (SIZE The rank indicator IE is Indicator (3)) present only if it is requested in the associated request. In that case Cf. TS 36.213 [7.2.3]. >>Wideband M BIT STRING (SIZE Cf. TS 36.213 [7.2.3]. CQI For (4)) Codeword 0 >>Wideband O BIT STRING (SIZE Cf. TS 36.213 [7.2.3]. CQI For (4)) Codeword 1 >>Subband CQI 0 . . . <maxCQI 0 indicates no subband List Subbands> CQI, which is always chosen if associated request does not want subband CQI, or this IE is present only if associated request wants subband CQI >>>Subband O BIT STRING (SIZE Cf. TS 36.213 [7.2.3]. CQI for (2)) codeword 0 >>>Subband O BIT STRING (SIZE Cf. TS 36.213 [7.2.3]. CQI for (2)) codeword 1 >>UE-CSI M FFS CSI process process configuration Configuration information. information Range bound Explanation maxUEsubsetCSIReport Maximum UE subset size for which UE-CSI can be reported. The value is 32. maxUE-CSIProcess Maximum number of CSI processes per-UE. The value is 4. maxCQISubbands Maximum number of subbands for UE CQI reporting. The value is 28.

Alternatively, the parameter maxUEsubsetCSIReport can be 8, 16, 32, 48, 64, or 256. Further, optionally, the UE-ID can have a more compact representation using say 8 bits or 6 bits or 5 bits (equivalently 256 or 64 or 32 possible indices from a configurable table).

Next, we consider the case when subband indices have to be indicated. This is important to accommodate feedback modes that involve UE selected subband feedback.

TABLE B4 IE type and Semantics IE/Group Name Presence Range reference description UE subset CSI Report 1 . . . <maxUEsubset CSIReport> >C-RNTI M BIT STRING ID of the UE served by (SIZE (16)) the cell in eNB₂. Defined in TS 36.331. >UE-CSI process 1 . . . information <maxUE-CSIprocess> >>Rank Indicator O BIT STRING The rank indicator IE is (SIZE (3)) present only if it is requested in the associated request. In that case Cf. TS 36.213 [7.2.3]. >>Wideband CQI For M BIT STRING Codeword 0 (SIZE (4)) >>Wideband CQI For O BIT STRING Codeword 1 (SIZE (4)) >>Subband CQI List 0 . . . <maxCQISubbands> This IE is present only if associated request wants subband CQI >>>Subband CQI O BIT STRING for codeword 0 (SIZE (4)) >>>Subband CQI O BIT STRING for codeword 1 (SIZE (4)) >>>Subband index O INTEGER Included in case of UE (0 . . . 27, . . . ) selected subband CQI reporting. >>UE-CSI process M FFS CSI process Configuration configuration information information.

Note that as an alternative in the above tables, for each CQI the bit string field of 4 bits (2 bits) can be replaced by INTEGER (0 . . . 15, . . . ) (INTEGER (0 . . . 7, . . . )).

In another alternative the sub band indices can be conveyed by means of a combinatorial index which is described next.

The idea here is that depending on the number of PRBs (or RBs (resource blocks) for short) in the downlink available at sending eNB2 (a parameter which is known or conveyed separately to the receiving eNB1), the set of all possible subband selections that can be made together with the subband size, for all feedback modes, can be deduced by eNB1.

For example when 110 RBs are available at eNB2 (and this number is conveyed to eNB1) eNB1 can deduce that for a UE configured under:

Aperiodic, Mode 2-*: 6 UE selected subband indices

A subframe is composed of 28 subbands. Among 28 subbands, 6 subbands are selected by the UE. The number of PRBs in the subbands is 4 except for the last one; the number of PRBs in the last subband is 2 (4*27+2=110).

For Aperiodic, Mode 3-*: 14 higher layer-configured sub bands

A subframe is composed of 14 subbands. The number of PRBs in the subband is 8 except for the last one; the number of PRBs in the last subband is 6 (8*13+6=110).

For Periodic, Mode 2-*: 4 UE selected subband indices (with an additional constraint on choosing one sub band per bandwidth portion or part)

A subframe is composed of 14 subbands. Among 14 subbands, 4 subbands are selected by the UE. The number of PRBs in the subbands is 8 except for the last one; the number of PRBs in the last subband is 6 (8*13+6=110).

Then, considering all possible feasible subband selections under all the aforementioned feedback modes, it is possible to assign a unique label to each distinct feasible selection of sub bands. All possible such labels together decide the range of a combinatorial index R. As a result, knowing the value of R the receiving eNB1 can deduce the subband selection. The associated CQIs (one for each subband in the indicated selection) can be ordered in the increasing order of the frequency range represented by the indicated subbands. Each such CQI can be conveyed using full representation (i.e., using 16 possibilities) which can then be directly used by the receiving eNB1.

TABLE B5 IE type and Semantics IE/Group Name Presence Range reference description UE subset CSI Report 1 . . . <maxUEsubsetCSIReport> >C-RNTI M BIT STRING ID of the UE (SIZE (16)) served by the cell in eNB₂. Defined in TS 36.331. >UE-CSI process 1 . . . information <maxUE-CSIprocess> >>Rank Indicator O BIT STRING The rank indicator (SIZE (3)) IE is present only if it is requested in the associated request. In that case Cf. TS 36.213 [7.2.3]. >>Wideband CQI For M BIT STRING Codeword 0 (SIZE (4)) >>Wideband CQI For O BIT STRING Codeword 1 (SIZE (4)) >>combinatorial O Integer FFS This IE is present index only if associated request wants subband CQI >>>Subband CQI List 0 . . . The number of <maxCQISubbands > subbands in the list as well as their respective indices and sizes are deduced from the combinatorial index. >>>>Subband CQI M BIT STRING for codeword 0 (SIZE (4)) >>>>Subband CQI O BIT STRING for codeword 1 (SIZE (4)) >>UE-CSI process M FFS CSI process Configuration configuration information information.

UE Configuration Independent Coding Structure

A coding structure for signaling CSI over X2 in a UE-configuration independent way is shown in Table I1. In this structure, a subband is defined as a set of contiguous PRBs having the same CQI value. The subband partitioning is left to the sending eNB2 implementation, and is not restricted by the UE's CSI reporting configuration. Each indicated CQI follows the definition of a 4 bit CQI (Cf. TS 36.213). This allows for the sending eNB2 to process the CSI it receives from the UE in any manner as long as each indicated CQI is consistent with the basic CQI definition. The receiving eNB1 can directly use these CQIs while being agnostic to how they were procured and processed by eNB1.

TABLE B6 UE configuration independent coding structure IE type and IE/Group Name Presence Range reference Semantics description CSI per UE 1 . . . <maxnoofUE-CSI> >C-RNTI M BIT STRING (SIZE (16)) >CSI per Interference 1 . . . Hypotheses <maxnoofInterfer- enceHypothesis > >>Interference Hypothesis M [FFS] Information >>Wideband CQI for M INTEGER Codeword 0 (0 . . . 15, . . . ) >>Wideband CQI for O INTEGER Codeword 1 (0 . . . 15, . . . ) >>Rank Indication M INTEGER Defined in TS 36.213 [11]. (1 . . . 8, . . . ) >>Subband CQI List 0 . . . Subbands are listed in the <maxnoofSubband> order of increasing frequency. >>>Subband Start O INTEGER PRB number of the first (0 . . . 109, . . . ) PRB in the subband. If this IE is not present, the subband is contiguous with the previous subband in the list, or starts with PRB 0 if this is the first subband in the list. >>>Subband Size O INTEGER Number of contiguous (1 . . . 110, . . . ) PRBs in the subband. If this IE is not present, the value is the same as the previous subband in the list. >>>Subband CQI for M INTEGER Codeword 0 (0 . . . 15, . . . ) >>>Subband CQI for O INTEGER Codeword 1 (0 . . . 15, . . . ) Range bound Explanation maxnoofUE-CSI Maximum number of UE-specific CSI reports. Value is 128 or 64 or 32 maxnoofInterferenceHypotheses Maximum number of Interference Hypotheses. Value is 4. maxnoofSubband Maximum number of Subbands. Value is 28.

We note here that reporting full (complete) CQI (with 16 possibilities) for each indicated subband CQI instead of differential CQI is useful since otherwise the receiving eNB1 may not know how to combine a corresponding wideband CQI and differential sub-band CQI (with fewer than 16 possibilities) in order to obtain the full CQI for that subband, for instance, in the case that the precise feedback mode configured for the UE of interest under that CSI process is not conveyed to the receiving eNB1. We note here also that it might be desirable to not impose restrictions on sending eNB2 on how it combines reports from multiple different feedback modes configured for that UE under the same CSI process. Then, note that when aperiodic feedback mode 3-1 is configured for the UE (by eNB2), the UE reported sub band CQI is encoded differentially with respect to the corresponding wideband CQI using 2 bits representing differential values {−2, 0, 1, 2}. On the other hand, in the case of aperiodic feedback mode 2-0 or 2-2, only the best M-average is reported by the UE by differentially encoding it with respect to a corresponding wideband CQI using 2 bits representing differential values {1, 2, 3, 4}. Further, in case of periodic feedback mode 2-1 the CQI corresponding to codeword-1 for each UE selected subband within a bandwidth part can itself be of 4 bits, whereas that of codeword-2 (when RI>1) is differentially encoded with respect to CQI of codeword-1 using 3 bits.

It becomes apparent from the above discussion that a transparent way of conveying CQI (without having to convey all details regarding to one or more feedback modes configured under that CSI process for that UE) is to allow for full (complete) CQI for each indicated subband.

Another issue that is important, is to ensure that the RI and CQIs conveyed by eNB2 to eNB1 in a UE CSI report are mutually consistent, i.e., all the reported CQIs are computed by the UE for the same RI (which is identical to the one in the Rank Indication IE when the latter is present). This issue is important to address because under certain feedback modes (such as periodic mode 2-1) the RI and the wideband CQI(s) as well as the subband CQI(s) for one or more bandwidth portions can be reported by the UE on different subframes. Thus, depending on the periodicity defined by eNB1 in its CSI request, it can happen that the latest RI available for the UE under the CSI process, can be different from the one for which the most recent CQI(s) are computed. In such a case, the sending eNB2 should ensure that its CSI report is consistent, for instance by using the RI value for which the most recently available CQI(s) have been computed.

The variation (which allows the requesting eNB to specify whether or not it wants to receive subband CQI(s) or Rank Indication is provided below. In this context, we note that since the requesting eNB1 has no control over how eNB2 configures CSI processes (and constituent feedback modes) for its users, it should be in any case able to exploit different type of CSI reports (wideband only or wideband and subband).

TABLE B7 IE type and IE/Group Name Presence Range reference Semantics description CSI per UE 1 . . . <maxnoofUE-CSI> >C-RNTI M BIT STRING (SIZE (16)) >CSI per Interference 1 . . . Hypotheses <maxnoofInterference- Hypothesis > >>Interference M [FFS] Hypothesis Information >>Wideband CQI for M INTEGER Codeword 0 (0 . . . 15, . . . ) >>Wideband CQI for O INTEGER Codeword 1 (0 . . . 15, . . . ) >>Rank Indication O INTEGER The rank indication IE is (1 . . . 8, . . . ) present only if it is requested in the associated request. In that case it follows the definition in TS 36.213 [11]. >>Subband CQI List 0 . . . This IE is present only if <maxnoofSubband> associated request wants subband CQI. In that case subbands are listed in the order of increasing frequency. >>>Subband Start O INTEGER PRB number of the first (0 . . . 109, . . . ) PRB in the subband. If this IE is not present, the subband is contiguous with the previous subband in the list, or starts with PRB 0 if this is the first subband in the list. >>>Subband Size O INTEGER Number of contiguous (1 . . . 110, . . . ) PRBs in the subband. If this IE is not present, the value is the same as the previous subband in the list. >>>Subband CQI for M INTEGER Codeword 0 (0 . . . 15, . . . ) >>>Subband CQI for O INTEGER Codeword 1 (0 . . . 15, . . . )

Another variation which allows for further simplification at the expense of not being bit efficient is as follows. Here the full CQIs for all possible subbands (which can be determined by the number of PRBs in the downlink available at eNB2) are always conveyed for a UE under the CSI process. In case the sub band CQI is not reported by a UE under the configured feedback mode for a subband, the sending eNB2 simply uses the corresponding wideband CQI value for that subband. Then, note that there is no need to include the wideband CQI(s) in case the associated request wants subband CQI.

9.2.19 Relative Narrowband Tx Power (RNTP)

This IE provides an indication on DL power restriction per PRB in a cell and other information needed by a neighbour eNB for interference aware scheduling.

TABLE B8 IE type IE/Group and Semantics Assigned Name Presence Range reference description Criticality Criticality RNTP Per M BIT Each position in — — PRB STRING the bitmap (6 . . . 110, . . . ) represents a n_(PRB) value (i.e. first bit = PRB 0 and so on), for which the bit value represents RNTP (n_(PRB)), defined in TS 36.213 [11]. Value 0 indicates “Tx not exceeding RNTP threshold”. Value 1 indicates “no promise on the Tx power is given”. This IE is used to indicate DL power restriction per PRB for the first subframe. In case the DL power restriction is static, the indicated DL power restriction is maintained over the subsequent subframes. RNTP M ENUMERATED RNTP_(threshold) is — — Threshold (−∞, defined in TS −11, −10, 36.213 [11]. −9, −8, −7, −6, −5, −4, −3, −2, −1, 0, 1, 2, 3, . . . ) Number Of M ENUMERATED P (number of — — Cell-specific (1, antenna ports for Antenna 2, 4, . . . ) cell-specific Ports reference signals) defined in TS 36.211 [10] P_B M INTEGER P_(B) is defined in TS — — (0 . . . 3, . . . ) 36.213 [11]. PDCCH M INTEGER Measured by — — Interference (0 . . . 4, . . . ) Predicted Number Impact Of Occupied PDCCH OFDM Symbols (see TS 36.211 [10]). Value 0 means “no prediction is available”. Extended M or O BIT Each position in RNTP Per STRING the bitmap PRB (6 . . . 4290, . . . ) represents a PRB in a subframe, for which value “1” indicates ‘interference protected resource’ or ‘no promise on the Tx power is given’ and value “0” indicates ‘resource with no utilization constraints’ or ‘Tx not exceeding RNTP threshold.’ The first bit corresponds to PRB 0 of the second or first subframe for which the extended RNTP per PRB IE is valid, the second bit corresponds to PRB 1 of the second or first subframe for which the extended RNTP per PRB IE is valid, and so on. The length of the bit string is an integer (maximum 39) multiple of N_(RB) ^(DL). N_(RB) ^(DL) is defined in TS 36.211 [10]. The bit string may span across multiple contiguous subframes. The pattern across contiguous subframes (formed by RNTP per PRB and extended RNTP per PRB) is continuously repeated. RNTP per 0 . . . 1 PRB start time >Starting M or O INTEGER Number of the first SFN (0 . . . 1023, . . . ) system frame from which the RNTP Per PRB (Per Subframe) IE is valid or SFN of the radio frame containing the first subframe when the RNTP Per PRB IE is valid. >Starting M or O INTEGER Index of the first Subframe (0 . . . 9, . . . ) subframe from Index which the RNTP Per PRB (Per Subframe) IE is valid or Subframe number, within the radio frame indicated by the Start SFN IE, of the first subframe when the RNTP Per PRB IE is valid.

An alternate Table for RNTP enhancement is given below.

TABLE B9 IE type IE/Group and Semantics Assigned Name Presence Range reference description Criticality Criticality RNTP per M BIT Each position in — — PRB STRING the bitmap (6 . . . 110, . . . ) represents a n_(PRB) value (i.e. first bit = PRB 0 and so on), for which the bit value represents RNTP (n_(PRB)), defined in TS 36.213 [11]. Value 0 indicates “Tx not exceeding RNTP threshold”. Value 1 indicates “no promise on the Tx power is given”. This IE is ignored if the RNTP per PRB per subframe IE is present. RNTP M ENUMERATED RNTP_(threshold) is — — Threshold (−∞, −11, defined in TS −10, −9, 36.213 [11]. −8, −7, −6, −5, −4, −3, −2, −1, 0, 1, 2, 3, . . . ) Number Of M ENUMERATED P (number of — — Cell-specific (1, 2, 4, . . . ) antenna ports for Antenna cell-specific Ports reference signals) defined in TS 36.211 [10] P_B M INTEGER P_(B) is defined in TS — — (0 . . . 3, . . . ) 36.213 [11]. PDCCH M INTEGER Measured by — — Interference (0 . . . 4, . . . ) Predicted Number Impact Of Occupied PDCCH OFDM Symbols (see TS 36.211 [10]). Value 0 means “no prediction is available”. RNTP Per O BIT Each position in PRB per STRING the bitmap subframe (6 . . . 4400, . . . ) represents a PRB in a subframe, for which value “1” indicates ‘no promise on the Tx power is given’ and value “0” indicates ‘Tx not exceeding RNTP threshold.’ The first bit corresponds to PRB 0 of the first subframe for which the RNTP per PRB per subframe IE is valid, the second bit corresponds to PRB 1 of the first subframe for which the RNTP per PRB per subframe IE is valid, and so on. The length of the bit string is an integer (maximum 40) multiple of N_(RB) ^(DL). N_(RB) ^(DL) is defined in TS 36.211 [10]. The bit string may span across multiple contiguous subframes. The pattern across contiguous subframes formed by RNTP per PRB per subframe IE is continuously repeated. RNTP per 0 . . . 1 PRB per subframe start time >Starting M INTEGER SFN of the radio SFN (0 . . . 1023, . . . ) frame containing the first subframe when the RNTP Per PRB Per Subframe IE is valid. >Starting M INTEGER Subframe number, Subframe (0 . . . 9, . . . ) within the radio Index frame indicated by the Start SFN IE, of the first subframe when the RNTP Per PRB Per Subframe IE is valid.

Another alternate Table for RNTP enhancement is given below.

TABLE B10 IE type IE/Group and Semantics Assigned Name Presence Range reference description Criticality Criticality RNTP per M BIT Each position in — — PRB STRING the bitmap (6 . . . 110, . . .) represents a n_(PRB) value (i.e. first bit = PRB 0 and so on), for which the bit value represents RNTP (n_(PRB)), defined in TS 36.213 [11]. Value 0 indicates “Tx not exceeding RNTP threshold”. Value 1 indicates “no promise on the Tx power is given”. This IE is ignored if the RNTP per PRB per subframe IE is present. RNTP M ENUMERATED RNTP_(threshold) is — — Threshold (−∞, −11, defined in TS −10, −9, −8, 36.213 [11]. −7, −6, −5, −4, −3, −2, −1, 0, 1, 2, 3, . . .) Number Of M ENUMERATED P (number of — — Cell-specific (1, 2, 4, . . .) antenna ports for Antenna cell-specific Ports reference signals) defined in TS 36.211 [10] P_B M INTEGER P_(B) is defined in TS — — (0 . . . 3, . . .) 36.213 [11]. PDCCH M INTEGER Measured by — — Interference (0 . . . 4, . . .) Predicted Number Impact Of Occupied PDCCH OFDM Symbols (see TS 36.211 [10]). Value 0 means “no prediction is available”. RNTP Per O BIT Each position in PRB per STRING the bitmap subframe (6 . . . 4400, . . .) represents a PRB in a subframe, for which value “1” indicates ‘resource with no utilization constraints’ and value “0” indicates ‘interference protected resource.’ The first bit corresponds to PRB 0 of the first subframe for which the RNTP per PRB per subframe IE is valid, the second bit corresponds to PRB 1 of the first subframe for which the RNTP per PRB per subframe IE is valid, and so on. The length of the bit string is an integer (maximum 40) multiple of N_(RB) ^(DL). N_(RB) ^(DL) is defined in TS 36.211 [10]. The bit string may span across multiple contiguous subframes. The pattern across contiguous subframes formed by RNTP per PRB per subframe IE is continuously repeated. RNTP per 0 . . . 1 PRB per subframe start time >Starting M INTEGER SFN of the radio SFN (0 . . . 1023, . . .) frame containing the first subframe when the RNTP Per PRB Per Subframe IE is valid. >Starting M INTEGER Subframe number, Subframe (0 . . . 9, . . .) within the radio Index frame indicated by the Start SFN IE, of the first subframe when the RNTP Per PRB Per Subframe IE is valid.

Another alternative using multiple thresholds conveyed via 2 bits is given below.

TABLE B11 IE type IE/Group and Semantics Assigned Name Presence Range reference description Criticality Criticality ERNTP Per M BIT Each position in — — PRB and STRING the bitmap subframe (12 . . . 220, . . .) represents a PRB in a subframe, for which the value “xx” indicates how the transmission power in a resource block is mapped relative to the two power thresholds: 00 - power level not exceeding the LPTH 01 - power level between LPTH and MPTH; 10 - power level between MPTH and HPTH; 11 - no promise on the Tx power is given. The first 2 bits correspond to PRB 0 of the first subframe for which the IE is valid, the following 2 bits correspond to PRB 1 of the first subframe for which the IE is valid, and so on. The bit string may span across multiple contiguous subframes. The length of the bit string is an integer (maximum 40) multiple of N_(RB) ^(DL). The parameter is defined in TS 36.211 [10]. The ERNTP pattern is continuously repeated with a periodicity indicated in Periodicity. Transmitted power levels LPTH (Low M ENUMERATED Lower RNTP — — Power (−∞, −11, power threshold, Threshold) −10, −9, −8, using the −7, −6, −5, −4, RNTP_(threshold) −3, −2, −1, 0, defined in TS 1, 2, 3, . . .) 36.213 [11]. MPTH M ENUMERATED Medium RNTP (Medium (−∞, −11, power threshold, Power −10, −9, −8, using the Threshold) −7, −6, −5, −4, RNTP_(threshold) −3, −2, −1, 0, defined in TS 1, 2, 3, . . .) 36.213 [11]. HPTH (High M ENUMERATED Higher RNTP Power (−∞ −11, power threshold, Threshold) −10, −9, −8, using the −7, −6, −5, −4, RNTP_(threshold) −3, −2, −1, 0, defined in TS 1, 2, 3, . . .) 36.213 [11]. Subframe sequence definition >Start SFN M INTEGER SFN of the radio (0 . . . 1023) frame containing the first subframe where the RNTP Per PRB Per Subframe IE is valid. >Start M INTEGER Subframe Subframe (0 . . . 39) number, within the Number radio frame indicated by the Start SFN IE, of the first subframe when the RNTP Per PRB Per Subframe IE is valid. No. of M 1 . . . 40 No. of subframes subframes for which is defined the bitstream Periodicity 1 . . . 40 The number of subframes after which the bit pattern is repeated Number Of M ENUMERATED P (number of Cell-specific (1, 2, 4, . . .) antenna ports for Antenna cell-specific Ports reference signals) defined in TS 36.211 [10] P_B M INTEGER P_(B) is defined in (0 . . . 3, . . .) TS 36.213 [11].

The point in the table given above is that since the choice ‘11’ already indicates no promise on the power level (which covers the case of transmit power being arbitrarily high) we can use three thresholds (instead of two) since there is no need to convey that the power level is greater than HPTH (as this is subsumed by ‘11’).

However, one problem with indicating multiple thresholds is that the current CoMP hypothesis (implicitly) assumes just one threshold. In this sense there is a mismatch between using multiple thresholds in eRNTP and not in the CoMP hypothesis. Consequently, the full potential of multiple thresholds may not be realized inspire of the additional overhead.

Embodiment C C1. Introduction

In the following we provide our views on CSI exchange, as well as proposals containing the required message structures.

C2. Discussion

C2.1 CSI Exchange: Configuring CSI Processes

From previous discussion it is evident that coordination among the eNBs is required in order to define a set of assignable CSI processes that have a consistent meaning Once the set of these CSI processes is defined, the CSI exchanged among eNBs should include the respective CSI process configuration information, in order to convey the conditions under which the CSI was measured by the UE. This configuration information should include CSI-RS-ConfigNZP [36.331b, Section 6.3.2] and CSI-IM-Config [36.331b, Section 6.3.2]. We note here that doing so would enable exchange of per-point CSI process (under which the UE estimates RS from any one point in its measurement set (or CoMP set) while the associated IMR measures the out of CoMP set or out of cluster interference) configuration. If one such process is sent to a receiving eNB for each point in that UE's measurement set, any interference hypothesis for that UE can be emulated by receiving eNB. This can indeed mitigate the bottleneck in terms defining enough CSI processes to cover sufficiently many interference hypotheses. One way of conveying this configuration information is through a look-up-table. A look-up-table mapping an index to each possible distinct CSI process configuration can be constructed (possibly separately for each eNB). Here, by a possible CSI process we mean a process that can be assigned to a served UE to measure its CSI. Such a table can be exchanged among neighbors first and from then on the configuration information can be exchanged via indices. The total number of defined processes (including their configuration information) in each table can be limited in order to limit signaling overhead. For instance, this number could be one of {7, 8, 9, 16, 32}. As an option, the configuration information for a process can also include power offset value Pc and/or offsets Pa and Pb, that were configured for that process. Further optionally, it can also indicate for which (if any) among the other processes, that process was set to be reference rank process. As an additional option, the configured feedback mode information (such as periodic or aperiodic) can also be included.

C2.2 CSI Exchange: Contents

One eNB can send CSI reports pertaining to one or more of its UEs to a neighboring eNB. For each UE, the CSI that the eNB sends to a neighbor can comprise:

CQI: up-to 2 CQIs, each including a wideband component and possible sub-band components

RI: one wideband component

We note that the PMI was excluded from the CSI exchange report [1]. The justification for this exclusion was to minimize the overhead and the fact that PMI can depend on fast changing channel information, thus reducing its utility over non ideal backhaul with a higher latency. However, in the absence of PMI the use of RI is limited. Indeed, any rank greater than 1 will convey only 2 CQI(s), one for each of the two codewords. No further information about the (average) spatial directions seen by that UE can be deduced by the eNB receiving the report. As a result, reporting the RI should be made optional. Moreover, the eNB requesting the CSI report (eNB1) should be able to specify whether or not it would like to receive RI reports. Similarly, the eNB requesting the CSI reports should be able to specify whether or not it requires subband specific CQI reports. This can be achieved by setting a bit (in the measurement request) to be 0 if rank is not requested and 1 otherwise. Another bit can be set to 0 if subband CQIs are not requested and 1 otherwise. In this context, we note that since the requesting eNB has no control over how the sending eNB (eNB2) configures CSI processes (and constituent feedback modes) for its users, it should be in any case able to exploit different type of CSI reports (wideband only or wideband and subband).

Proposal: Include optional IE in resource status request indicating whether RI and/or subband CQI should be sent in the resource status response message.

Implementation based processing of the short-term CSI (received via over-the-air signaling) by the sending eNB, prior to CSI exchange has been agreed. In this context, we believe that reporting full (complete) CQI (with 16 possibilities), where each such CQI follows the definition of a 4 bit CQI (Cf. TS 36.213), for each indicated subband instead of differential CQI is useful. This has main two advantages. It allows the sending eNB full freedom in obtaining these CQIs. Indeed, it is desirable to not impose restrictions on sending eNB2 on how it processes or combines reports from multiple different feedback modes configured for a UE under the same CSI process. Secondly, the receiving eNB can be agnostic to the configured feedback modes. This latter point is important because when aperiodic feedback mode 3-1 is configured for the UE (by eNB2), the UE reported sub band CQI is encoded differentially with respect to the corresponding wideband CQI using 2 bits representing differential values {−2, 0, 1, 2}. On the other hand, in the case of aperiodic feedback mode 2-0 or 2-2, only the best M-average CQI is reported by the UE by differentially encoding it with respect to a corresponding wideband CQI, using 2 bits representing differential values {1, 2, 3, 4}. Further, in case of periodic feedback mode 2-1 the CQI corresponding to codeword-1 for each UE selected subband within a bandwidth part can itself be of 4 bits, whereas that of codeword-2 (when RI>1) is differentially encoded with respect to CQI of codeword-1 using 3 bits.

It becomes apparent from the above discussion that a transparent way of conveying CQI (without having to convey all details regarding to one or more feedback modes configured under that CSI process for that UE) is to allow for full (complete) CQI for each indicated subband.

Proposal: Convey each subband CQI using full representation (4 bits or 16 possibilities)

Next, we consider subband indexing and propose an alternative in which the subband selection (including their sizes, indices) is conveyed by means of a combinatorial index which is described next.

This idea is a simple extension of that used in TS 36.213 for aperiodic feedback mode 2-*. In particular, depending on the number of PRBs (or RBs for short) in the downlink available at sending eNB2 (a parameter which is known or conveyed separately to the receiving eNB1), the set of all possible subband selections that can be made together with the subband sizes for all feedback modes can be deduced by eNB1.

For example when 110 RBs are available at eNB2 (and this number is conveyed to eNB1) eNB1 can deduce that for a UE configured under:

Aperiodic, Mode 2-*: 6 UE selected subband indices

A subframe is composed of 28 subbands. Among 28 subbands, 6 subbands are selected by the UE. The number of PRBs in the subbands is 4 except for the last one; the number of PRBs in the last subband is 2 (4*27+2=110).

For Aperiodic, Mode 3-*: 14 higher layer-configured sub bands

A subframe is composed of 14 subbands. The number of PRBs in the subband is 8 except for the last one; the number of PRBs in the last subband is 6 (8*13+6=110).

For Periodic, Mode 2-*: 4 UE selected subband indices (with an additional constraint on choosing one sub band per bandwidth portion or part)

A subframe is composed of 14 subbands. Among 14 subbands, 4 subbands are selected by the UE. The number of PRBs in the subbands is 8 except for the last one; the number of PRBs in the last subband is 6 (8*13+6=110).

Then, considering all possible feasible subband selections under all the aforementioned feedback modes, it is possible to assign a unique label to each distinct feasible selection of sub bands. All possible such labels together decide the range of a combinatorial index R. As a result, knowing the value of R the receiving eNB can deduce the subband selection. The associated CQIs (one for each subband in the indicated selection) can be ordered in the increasing order of the frequency range represented by the indicated subbands. Each such CQI can be conveyed using full representation (i.e., using 16 possibilities) which can then be directly used by the receiving eNB1.

Proposal: Convey subband indexing and size information via a combinatorial index.

Another issue that is important, is to ensure that the RI and CQIs conveyed by eNB2 to eNB1 in a UE CSI report are mutually consistent, i.e., all the reported CQIs are computed by the UE for the same RI (which is identical to the one in the Rank Indication IE when the latter is present). This issue is important to address because under certain feedback modes (such as periodic mode 2-1) the RI and the wideband CQI(s) as well as the subband CQI(s) for one or more bandwidth portions can be reported by the UE on different subframes. Thus, depending on the periodicity defined by eNB1 in its CSI request, it can happen that the latest RI available for the UE under the CSI process, can be different from the one for which one or more of the most recently available CQI(s) are computed. In such a case, the sending eNB2 should ensure that its CSI report is consistent, for instance by using the RI value for which the most recently available CQI(s) have been computed.

Proposal: Sending eNB must ensure RI and CQI(s) conveyed in a CSI report are mutually consistent.

One of the goals of CSI exchange is to facilitate centralized RRM. In a scenario with centralized RRM, the central node receiving the CSI reports should be able to keep track of the CSI information received for each particular UE, over all the received CSI reports. In order to ensure this, it has been agreed that a UE identifier will be included in each CSI report for each UE whose CSI is conveyed in that report. This ID should enable the receiving node to deduce which ones among all the reports that it receives, belongs to that user, thereby facilitating RRM. Including a similar UE ID in the reference signal received power (RSRP) reports will also be beneficial and allow the receiving eNB to combine or jointly exploit these two sets of reports.

Proposal: Include UE ID in RSRP measurement report

Proposals:

9.1.2.11 RESOURCE STATUS REQUEST

This message is sent by an eNB₁ to a neighbouring eNB₂ to initiate the requested measurement according to the parameters given in the message.

Direction: eNB₁→eNB₂.

TABLE C1 IE/Group IE type and Semantics Assigned Name Presence Range reference description Criticality Criticality Message M 9.2.13 YES reject Type eNB1 M INTEGER Allocated by YES reject Measurement (1 . . . 4095, . . . ) eNB₁ ID eNB2 C-ifRegistrationRequestStop INTEGER Allocated by YES ignore Measurement (1 . . . 4095, . . . ) eNB₂ ID Registration M ENUMERATED A value set to YES reject Request (start, “stop”, stop, . . . ) indicates a request to stop all cells measurements. Report O BITSTRING Each position YES reject Characteristics (SIZE(32)) in the bitmap indicates measurement object the eNB₂ is requested to report. First Bit = PRB Periodic, Second Bit = TNL load Ind Periodic, Third Bit = HW Load Ind Periodic, Fourth Bit = Composite Available Capacity Periodic, this bit should be set to 1 if at least one of the First, Second or Third bits is set to 1, Fifth Bit = ABS Status Periodic, Xth Bit = UE-CSI Periodic. Other bits shall be ignored by the eNB₂. Cell To 1 Cell ID list for YES ignore Report which measurement is needed >Cell To 1 . . . <maxCellineNB> EACH ignore Report Item >>Cell ID M ECGI — — 9.2.14 Reporting O ENUMERATED YES ignore Periodicity (1000 ms, 2000 ms, 5000 ms, 10000 ms, . . . ) Partial O ENUMERATED Included if YES ignore Success (partial partial Indicator success success is allowed, . . . ) allowed CSI O BITSTRING Each position YES ignore Measurement (SIZE(2)) in the bitmap Report type indicates the type of CSI measurement to report. First bit = Rank, Second bit = subband CQI. Reporting O ENUMERATED Periodicity for YES ignore Periodicity of (5 ms, CSI CSI 10 ms, Measurement Measurement 20 ms, 40 ms, Report Report 80 ms, Periodic aperiodic, . . . ) Explanation Condition ifRegistrationRequestStop This IE shall be present if the Registration Request IE is set to the value “stop”. Range bound maxCellineNB Maximum no. cells that can be served by an eNB. Value is 256.

9.1.2.14 RESOURCE STATUS UPDATE

This message is sent by eNB₂ to neighbouring eNB₁ to report the results of the requested measurements.

Direction: eNB₂→eNB₁.

9.2.aa UE-CSI Report

This IE provides UE-CSI information for a set of UEs served by eNB₂.

TABLE C2 IE type and Semantics IE/Group Name Presence Range reference description CSI Report per UE 1 . . . <maxUEReport> >UE ID M BIT STRING ID of the UE (SIZE (16)) served by the cell in eNB₂. >CSI report per CSI 1 . . . process <maxCSIprocess> >>Rank Indicator O INTEGER The rank indicator (1 . . . 8, . . . ) IE is present only if it is requested in the associated request. In that case Cf. TS 36.213 [7.2.3]. >>Wideband CQI For M INTEGER Codeword 0 (0 . . . 15, . . . ) >>Wideband CQI For O INTEGER Codeword 1 (0 . . . 15, . . . ) >>combinatorial O Integer FFS This IE is present index only if associated request wants subband CQI >>>Subband CQI List 0 . . . The number of <maxCQISubbands > subbands in the list as well as their respective indices and sizes are deduced from the combinatorial index. Subband CQIs are sorted in the order of increasing frequency. >>>>Subband CQI M INTEGER for codeword 0 (0 . . . 15, . . . ) >>>>Subband CQI O INTEGER for codeword 1 (0 . . . 15, . . . ) >>UE-CSI process M FFS CSI process Configuration configuration information information.

We now consider eRNTP exchange.

It has been agreed that eRNTP will be delivered with the Load Information message.

In the following, we provide our views on content of this message, as well as a proposal.

C3. Discussion

C3.1 eRNTP Exchange

One concern is that a receiving eNB does not have the means to differentiate the “meaning” of the CoMP hypothesis. In particular, a potential issue is that the signaled hypothesis could be a “suggestion” by the sender or an “action” which implies that the pattern in the hypothesis will be applied. A proposed solution to this issue is to introduce an indicator IE in the CoMP Information IE to convey that the constituent resource allocation is an action. This proposal can be useful if a common pre-configured threshold is used (or implicitly assumed) with or with our this indicator IE. In other words, the “suggestion for” as well as the “action” by an eNB (or cell) are based on a common threshold (pre-configured for that eNB or cell and known to its neighbors). Another slightly more preferable option is to enhance and use the existing RNTP in order to convey the “action”. The enhancements can be done in two ways. The contents are captured in two corresponding proposals attached in the sequel.

The first presented proposal is based on a single threshold and exploits that fact that the RNTP (i.e., downlink (DL) power restriction) for the first subframe (subframe #0) is always conveyed. Then, if no information about the DL power restriction on any subsequent subframe is conveyed, the one conveyed for the first subframe can be assumed to remain static (i.e., applicable over subsequent subframes).

The second proposal is based one multiple thresholds. The point here is that since the choice ‘11’ already indicates no promise on the power level (which covers the case of transmit power being arbitrarily high) we can use three thresholds (instead of two), since there is no need to convey that the power level is greater than HPTH (as this is subsumed by ‘11’)

Proposal:

9.2.19 Relative Narrowband Tx Power (RNTP)

This IE provides an indication on DL power restriction per PRB in a cell and other information needed by a neighbour eNB for interference aware scheduling.

TABLE C3 IE/Group IE type and Semantics Assigned Name Presence Range reference description Criticality Criticality RNTP Per PRB M BIT STRING Each position in — — (6 . . . 110, . . . ) the bitmap represents a n_(PRB) value (i.e. first bit = PRB 0 and so on), for which the bit value represents RNTP (n_(PRB)), defined in TS 36.213 [11]. Value 0 indicates “Tx not exceeding RNTP threshold”. Value 1 indicates “no promise on the Tx power is given”. This IE is used to indicate DL power restriction per PRB for the first subframe. In case the DL power restriction is static, the indicated DL power restriction is maintained over the subsequent subframes. RNTP M ENUMERATED RNTP_(threshold) is — — Threshold (−∞, −11, defined in TS −10, −9, −8, −7, 36.213 [11]. −6, −5, −4, −3, −2, −1, 0, 1, 2, 3, . . . ) Number Of M ENUMERATED P (number of — — Cell-specific (1, 2, 4, . . . ) antenna ports for Antenna Ports cell-specific reference signals) defined in TS 36.211 [10] P_B M INTEGER P_(B) is defined in TS — — (0. . . 3, . . . ) 36.213 [11]. PDCCH M INTEGER Measured by — — Interference (0 . . . 4, . . . ) Predicted Number Impact Of Occupied PDCCH OFDM Symbols (see TS 36.211 [10]). Value 0 means “no prediction is available”. Extended O BIT STRING Each position in RNTP Per (6 . . . 4290, . . . ) the bitmap PRB represents a PRB in a subframe, for which value “1” indicates ‘no promise on the Tx power is given’ and value “0” indicates ‘Tx not exceeding RNTP threshold.’ The first bit corresponds to PRB 0 of the first subframe for which the extended RNTP per PRB IE is valid, the second bit corresponds to PRB 1 of the first subframe for which the extended RNTP per PRB IE is valid, and so on. The length of the bit string is an integer (maximum 39) multiple of nDLRB, which is defined in TS 36.211 [10]. The bit string may span across multiple contiguous subframes. The pattern across contiguous subframes (formed by RNTP per PRB and extended RNTP per PRB) is continuously repeated RNTP per 0 . . . 1 PRB start time >Starting SFN M INTEGER SFN of the radio (0 . . . 1023, . . . ) frame containing the first subframe when the RNTP Per PRB IE is valid. >Starting M INTEGER Subframe number, Subframe (0 . . . 9, . . . ) within the radio Index frame indicated by the Start SFN IE, of the first subframe when the RNTP Per PRB IE is valid.

The second alternative is given below.

TABLE C4 IE/Group IE type and Semantics Assigned Name Presence Range reference description Criticality Criticality ERNTP Per M BIT STRING Each position in — — PRB and (12 . . . 220, . . . ) the bitmap subframe represents a PRB in a subframe, for which the value “xx” indicates how the transmission power in a resource block is mapped relative to the three power thresholds: 00—power level not exceeding the LPTH 01—power level between LPTH and MPTH; 10—power level between MPTH and HPTH; 11—no promise on the Tx power is given. The first 2 bits correspond to PRB 0 of the first subframe for which the IE is valid, the following 2 bits correspond to PRB 1 of the first subframe for which the IE is valid, and so on. The bit string may span across multiple contiguous subframes. The length of the bit string is an integer (maximum 40) multiple of nDLRB. The parameter is defined in TS 36.211 [10]. The ERNTP pattern is continuously repeated with a periodicity indicated in Periodicity. Transmitted power levels LPTH (Low M ENUMERATED Lower RNTP — — Power (−∞, −11, power threshold, Threshold) −10, −9, −8, using the −7, −6, −5, −4, RNTP_(threshold) −3, −2, −1, 0, defined in TS 1, 2, 3, . . . ) 36.213 [11]. MPTH M ENUMERATED Medium RNTP (Medium (−∞, −11, power threshold, Power −10, −9, −8, using the Threshold) −7, −6, −5, −4, RNTP_(threshold) −3, −2, −1, 0, defined in TS 1, 2, 3, . . . ) 36.213 [11]. HPTH (High M ENUMERATED Higher RNTP Power (−∞, −11, power threshold, Threshold) −10, −9, −8, using the −7, −6, −5, −4, RNTP_(threshold) −3, −2, −1, 0, defined in TS 1, 2, 3, . . . ) 36.213 [11]. Subframe sequence definition >Start SFN M INTEGER SFN of the radio (0 . . . 1023) frame containing the first subframe where the RNTP Per PRB Per Subframe IE is valid. >Start M INTEGER Subframe Subframe (0 . . . 39) number, within Number the radio frame indicated by the Start SFN IE, of the first subframe when the RNTP Per PRB Per Subframe IE is valid. No. of M 1 . . . 40 No. of subframes subframes for which is defined the bitstream Periodicity 1 . . . 40 The number of subframes after which the bit pattern is repeated Number Of M ENUMERATED P (number of Cell-specific (1, 2, 4, . . . ) antenna ports for Antenna Ports cell-specific reference signals) defined in TS 36.211 [10] P_B M INTEGER P_(B) is defined in (0 . . . 3, . . . ) TS 36.213 [11].

Embodiment D D1. Introduction

In the following we provide our views on CSI and eRNTP exchange, as well as proposals containing the required message structures.

D2. Discussion

D2.1 CSI Exchange: Configuring CSI Processes

The concept of CSI processes was defined in Rel.11 to enable CSI feedback from a UE to its serving eNB. The CSI feedback is determined for each CSI process according to the serving TP and interference hypothesis configured in that process. Each CSI process that is configured for a UE, comprises a set of resource elements on which non-zero power CSI-RSs are sent and a channel estimate is obtained by that UE using observations received on those resource elements.

In addition, a set of resource elements is also indicated by the CSI process (referred to as interference measurement resources (IMRs)) on which the UE estimates the covariance of the interference it observes. The channel and covariance estimates are together used by the UE to determine and send its feedback report corresponding to that CSI process. Multiple such CSI processes (up-to 4) can be configured for a UE, each process corresponding to a different choice of signal or interference hypothesis. Moreover, in the scenario in which fast switching of the serving TP is not possible, different CSI processes that are configured for any given UE typically correspond to different choices of interference hypothesis.

Note from the brief discussion above that in the event the interference hypothesis of a configured CSI process presumes muting from a TP (that is a dominant interferer for the UE of interest) which is controlled by the neighboring eNB, coordination among the eNBs is required in order to ensure that the interference estimated by the UE on the constituent IMRs is consistent with the assumed hypothesis. Another similar event that requires coordination is if the non-zero power CSI-RSs indicated in the CSI process must be interference protected in order to ensure reliable channel estimation at the UE. In both these events, the dominant interferer that is controlled by the neighboring eNB must be muted on certain resource elements. Thus, a mechanism (with appropriate signaling) should be available to share the CSI-RS (comprising non-zero power CSI-RSs and IMRs) configurations between eNBs, which would facilitate configuration of CSI processes across multiple eNBs.

Once the CSI processes are configured, the CSI exchanged among eNBs over the backhaul should include the respective CSI process configuration information, in order to convey the conditions under which the CSI was measured by the UE. This configuration information includes non-zero power CSI-RS information and IMR information (comprising the subframe indices and zero-power CSI-RS information). Since this configuration is anyway informed to the UE via RRC (or higher layer) signaling, the same information can be reused as a container to convey the configuration to the neighboring eNB.

Another way of conveying this configuration information is through a look-up-table. A look-up-table mapping an index to one or more distinct applied CSI process configurations can be constructed for each eNB. Here, by an applied CSI process we mean a process that is used by at-least one UE served by that eNB to measure its CSI. Such a table can be exchanged among neighbors first and from then on the configuration information can be exchanged via indices. The total number of configurations in the table can be limited in order to limit signaling overhead.

Suitable values for the number of configurations in this table are either 8 or 16 or 32.

D2.2 CSI Exchange: Contents

One eNB can send CSI report pertaining to one or more of UEs to a neighboring eNB. For each UE, the CSI that the eNB sends to a neighbor can comprise:

CQI: up-to 2 CQIs, each including a wideband component and possible sub-band differential components

RI: one wideband component

We note that the PMI was excluded from the CSI exchange report [1]. The justification for this exclusion was to minimize the overhead and the fact that PMI can depend on fast changing channel information, thus reducing its utility over non ideal backhaul with a higher latency. However, in the absence of PMI the use of RI is limited. Indeed, any rank greater than 1 will convey only 2 CQI(s), one for each of the two codewords. No further information about the (average) spatial directions seen by that UE can be deduced by the eNB receiving the report. As a result, reporting the RI should be made optional. Moreover, the eNB requesting the CSI report should be able to specify whether or not it would like to receive RI reports. Similarly, the eNB requesting the CSI reports should be able to specify whether or not it requires subband specific CQI reports. This can be achieved by setting a bit (in the measurement request) to be 0 if rank is not requested and 1 otherwise. Another bit can be set to 0 if subband CQIs are not requested and 1 otherwise.

Processing (filtering or subsampling) of the short-term CSI (received via over-the-air signaling) at an eNB prior to exchange should be permitted.

One use case for this is when the periodicity of the CSI report that is requested by eNB1 to its neighbor eNB2, is larger than the over-the-air CSI signaling periodicity configured by eNB2. In this case eNB2 has to do some processing (such as subsampling or averaging) of the reports it receives before it sends it to eNB1. In this context, we note that the subsampling employed by eNB2 should be understood by eNB1 (if needed additional signaling can be added to ensure this). One possible way this can be accomplished (without any signaling overhead) is for eNB2 to use the subsampling factor determined by a pre-determined rule (known to or configured for all eNBs in advance) that outputs a subsampling factor, given the requested periodicity and CSI process configuration as inputs. On the other hand, averaging or scaling or filtering employed by eNB2 can be transparent to the receiving eNB1.

One of the goals of CSI exchange is to facilitate centralized RRM [3]. In a scenario with centralized RRM, the central node receiving the CSI reports should be able to keep track of the CSI information received for each particular UE, over all the received CSI reports. This can be achieved by including a UE identifier in each CSI report for each UE whose CSI is conveyed in that report. We want to include a unique ID for each user so that the receiving node knows which ones among all the reports that it receives, belong that user. This will be useful for RRM. Otherwise the receiving eNB will regard each received report as belonging to a distinct user. This can lead to sub-optimal resource allocation.

D2.3 eRNTP Exchange

Our view on eRNTP exchange is captured in a corresponding proposal attached in the end of this embodiment.

We note that the RNTP (i.e., downlink (DL) power restriction) for the first subframe is always conveyed. If no information about the DL power restriction on any subsequent subframe is conveyed, then the one conveyed for the first subframe can be assumed to remain static (i.e., applicable over subsequent subframes).

We also present several variations, one of which includes the use of multiple thresholds

D3. Conclusion

We discussed the necessary X2 message to support CSI and eRNTP exchange for inter-eNB CoMP and presented corresponding proposals.

Proposal:

9.1.2.11 RESOURCE STATUS REQUEST

This message is sent by an eNB₁ to a neighbouring eNB₂ to initiate the requested measurement according to the parameters given in the message.

Direction: eNB₁→eNB₂.

TABLE D1 IE/Group IE type and Semantics Assigned Name Presence Range reference description Criticality Criticality Message Type M 9.2.13 YES reject eNB1 M INTEGER Allocated by YES reject Measurement (1 . . . 4095, . . . ) eNB₁ ID eNB2 C-ifRegistrationRequestStop INTEGER Allocated by YES ignore Measurement (1 . . . 4095, . . . ) eNB₂ ID Registration M ENUMERATED A value set to YES reject Request (start, “stop”, indicates stop, . . . ) a request to stop all cells measurements. Report O BITSTRING Each position in YES reject Characteristics (SIZE(32)) the bitmap indicates measurement object the eNB₂ is requested to report. First Bit = PRB Periodic, Second Bit = TNL load Ind Periodic, Third Bit = HW Load Ind Periodic, Fourth Bit = Composite Available Capacity Periodic, this bit should be set to 1 if at least one of the First, Second or Third bits is set to 1, Fifth Bit = ABS Status Periodic, Xth Bit = UE-CSI Periodic. Other bits shall be ignored by the eNB₂. Cell To 1 Cell ID list for YES ignore Report which measurement is needed >Cell To 1 . . . <maxCellineNB> EACH ignore Report Item >>Cell ID M ECGI — — 9.2.14 Reporting O ENUMERATED YES ignore Periodicity (1000 ms, 2000 ms, 5000 ms, 10000 ms, . . . ) Partial O ENUMERATED Included if YES ignore Success (partial partial success Indicator success is allowed allowed, . . . ) CSI O BITSTRING Each position in YES ignore Measurement (SIZE(2)) the bitmap Report type indicates the type of CSI measurement to report. First bit = Rank, Second bit = subband CQI. ((Reporting O ENUMERATED Periodicity for YES ignore Periodicity of (5 ms, CSI CSI 10 ms, Measurement Measurement 20 ms, 40 ms, Report Periodic Report 80 ms, aperiodic, . . . ) Explanation Range bound maxCellineNB Maximum no. cells that can be served by an eNB. Value is 256. Condition ifRegistrationRequestStop This IE shall be present if the Registration Request IE is set to the value “stop”.

9.1.2.14 RESOURCE STATUS UPDATE

This message is sent by eNB₂ to neighbouring eNB₁ to report the results of the requested measurements.

Direction: eNB₂→eNB₁.

TABLE D2 IE/Group IE type and Semantics Assigned Name Presence Range reference description Criticality Criticality Message Type M 9.2.13 YES ignore eNB1 M INTEGER Allocated by YES reject Measurement (1 . . . 4095, . . . ) eNB₁ ID eNB2 M INTEGER Allocated by YES reject Measurement (1 . . . 4095, . . . ) eNB₂ ID Cell 1 YES ignore Measurement Result >Cell 1 . . . <maxCellineNB> EACH ignore Measurement Result Item >>Cell ID M ECGI 9.2.14 >>Hardware O 9.2.34 Load Indicator >>S1 TNL O 9.2.35 Load Indicator >>Radio O 9.2.37 Resource Status >>Composite O 9.2.44 YES ignore Available Capacity Group >>ABS O 9.2.58 YES ignore Status >> UE-CSI O 9.2.x1 YES ignore Report Range bound Explanation maxCellineNB Maximum no. cells that can be served by an eNB. Value is 256.

9.2.x1 UE-CSI Report

This IE provides UE-CSI information for a set of UEs served by eNB₂.

TABLE D3 IE/Group IE type and Semantics Name Presence Range reference description UE subset CSI 1 . . . Report <maxUEsubsetCSIReport> >UE ID M BIT STRING ID of the UE (SIZE (16)) served by the cell in eNB₂. >UE-CSI 1 . . . <maxUE-CSIprocess> process information >Rank O BIT STRING The rank indicator Indicator (SIZE (3)) IE is present only if it is requested in the associated request. In that case Cf. TS 36.213 [7.2.3]. >>Wideband M BIT STRING Cf. TS 36.213 CQI For (SIZE (4)) [7.2.3]. Codeword 0 >>Wideband O BIT STRING Cf. TS 36.213 d CQI For (SIZE (4)) [7.2.3]. Codeword 1 >>Subband 0 . . . <maxCQISubbands> This IE is present CQI List only if associated request wants subband CQI >>>Subband O BIT STRING Cf. TS 36.213 CQI for (SIZE (2)) [7.2.3]. codeword 0 >>>Subband O BIT STRING Cf. TS 36.213 CQI for (SIZE (2)) [7.2.3]. codeword 1 >>UE-CSI M FFS CSI process process configuration Configuration information. information Range bound Explanation maxUEsubsetCSIReport Maximum UE subset size for which UE-CSI can be reported. The value is 32. maxUE-CSIProcess Maximum number of CSI processes per-UE. The value is 4. maxCQISubbands Maximum number of subbands for UE CQI reporting. The value is 28.

Alternatively, the parameter maxUEsubsetCSIReport can be 8 or 64. Further, optionally, the UE-ID can have a more compact representation using say 8 bits or 6 bits or 5 bits (equivalently 256 or 64 or 32 possible indices from a configurable table).

Next, we consider the case when subband indices have to be indicated. This is important to accommodate feedback modes that involve UE selected subband feedback.

TABLE D4 IE type and Semantics IE/Group Name Presence Range reference description UE subset CSI Report 1 . . . <maxUEsubsetCSIReport> >C-RNTI M BIT STRING ID of the UE (SIZE (16)) served by the cell in eNB₂. Defined in TS 36.331. >UE-CSI process 1 . . . information <maxUE-CSIprocess> >>Rank Indicator O BIT STRING The rank indicator (SIZE (3)) IE is present only if it is requested in the associated request. In that case Cf. TS 36.213 [7.2.3]. >>Wideband CQI For M BIT STRING Codeword 0 (SIZE (4)) >>Wideband CQI For O BIT STRING Codeword 1 (SIZE (4)) >>Subband CQI List 0 . . . <maxCQISubbands> This IE is present only if associated request wants subband CQI >>>Subband CQI for O BIT STRING codeword 0 (SIZE (4)) >>>Subband CQI for O BIT STRING codeword 1 (SIZE (4)) >>>Subband index O INTEGER Included in case of (0 . . . 27, . . . ) UE selected subband CQI reporting. >>UE-CSI process M FFS CSI process Configuration configuration information information.

Note that as an alternative in the above tables, for each CQI the bit string field of 4 bits (2 bits) can be replaced by INTEGER (0 . . . 15, . . . ) (INTEGER (0 . . . 7, . . . )).

In another alternative the sub band indices can be conveyed by means of a combinatorial index which is described next.

The idea here is that depending on the number of PRBs (or RBs for short) in the downlink available at sending eNB2 (a parameter which is known or conveyed separately to the receiving eNB1), the set of all possible subband selections that can be made together with the subband size for each feedback mode can be deduced by eNB1.

For example when 110 RBs are available at eNB2 (and this number is conveyed to eNB1) eNB1 can deduce that for a UE configured under:

Aperiodic, Mode 2-*: 6 UE selected subband indices

A subframe is composed of 28 subbands. Among 28 subbands, 6 subbands are selected by the UE. The number of PRBs in the subbands is 4 except for the last one; the number of PRBs in the last subband is 2 (4*27+2=110).

For Aperiodic, Mode 3-*: 14 higher layer-configured sub bands

A subframe is composed of 14 subbands. The number of PRBs in the subband is 8 except for the last one; the number of PRBs in the last subband is 6 (8*13+6=110).

For Periodic, Mode 2-*: 4 UE selected subband indices (with an additional constraint on choosing one sub band per bandwidth portion or part)

A subframe is composed of 14 subbands. Among 14 subbands, 4 subbands are selected by the UE. The number of PRBs in the subbands is 8 except for the last one; the number of PRBs in the last subband is 6 (8*13+6=110).

Then, considering all possible feasible subband selections under all the aforementioned feedback modes, it is possible to assign a unique label to each distinct feasible selection of sub bands. All possible such labels together decide the range of a combinatorial index R. As a result, knowing the value of R the receiving eNB can deduce the subband selection. The associated CQIs (one for each subband in the indicated selection) can be ordered in the increasing order of the frequency range represented by the indicated subbands. Each such CQI can be conveyed using full representation (i.e., using 16 possibilities) which can then be directly used by the receiving eNB1.

TABLE D5 IE type and Semantics IE/Group Name Presence Range reference description UE subset CSI Report 1 . . . <maxUEsubsetCSIReport> >C-RNTI M BIT STRING ID of the UE (SIZE (16)) served by the cell in eNB₂. Defined in TS 36.331. >UE-CSI process 1 . . . information <maxUE-CSIprocess> >>Rank Indicator O BIT STRING The rank indicator (SIZE (3)) IE is present only if it is requested in the associated request. In that case Cf. TS 36.213 [7.2.3]. >>Wideband CQI For M BIT STRING Codeword 0 (SIZE (4)) >>Wideband CQI For O BIT STRING Codeword 1 (SIZE (4)) >> combinatorial O Integer FFS This IE is present index only if associated request wants subband CQI >>>Subband CQI List 0 . . . <maxCQISubbands> The number of subbands in the list as well as their respective indices and sizes are deduced from the combinatorial index. >>>>Subband CQI M BIT STRING for codeword 0 (SIZE (4)) >>>>Subband CQI O BIT STRING for codeword 1 (SIZE (4)) >>UE-CSI process M FFS CSI process Configuration configuration information information.

UE Configuration Independent Coding Structure

A coding structure for signaling CSI over X2 in a UE-configuration independent way is shown in Table I1. In this structure, a subband is defined as a set of contiguous PRBs having the same CQI value. The subband partitioning is left to the sending eNB2 implementation, and is not restricted by the UE's CSI reporting configuration. Each indicated CQI follows the definition of a 4 bit CQI (Cf. TS 36.213). This allows for the sending eNB2 to process the CSI it receives from the UE in any manner as long as each indicated CQI is consistent with the basic CQI definition. The receiving eNB1 can directly use these CQIs while being agnostic to how they were procured and processed by eNB1.

TABLE D6 UE configuration independent coding structure IE type and Semantics IE/Group Name Presence Range reference description CSI per UE 1 . . . <maxnoofUE-CSI> >C-RNTI M BIT STRING (SIZE (16)) >CSI per Interference 1 . . . Hypotheses <maxnoofInterferenceHypothesis> >>Interference Hypothesis M [FFS] Information >>Wideband CQI for M INTEGER(0 . . . Codeword 0 15, . . . ) >>Wideband CQI for O INTEGER(0 . . . Codeword 1 15, . . . ) >>Rank Indication M INTEGER(1 . . . Defined in TS 8, . . . ) 36.213 [11]. >>Subband CQI List 0 . . . Subbands are listed <maxnoofSubband> in the order of increasing frequency. >>>Subband Start O INTEGER(0 . . . PRB number of the 109, . . . ) first PRB in the subband. If this IE is not present, the subband is contiguous with the previous subband in the list, or starts with PRB 0 if this is the first subband in the list. >>>Subband Size O INTEGER(1 . . . Number of 110, . . . ) contiguous PRBs in the subband. If this IE is not present, the value is the same as the previous subband in the list. >>>Subband CQI for M INTEGER(0 . . . Codeword 0 15, . . . ) >>>Subband CQI for O INTEGER(0 . . . Codeword 1 15, . . . )

We note here that reporting full (complete) CQI (with 16 possibilities) for each indicated subband CQI instead of differential CQI is useful since otherwise the receiving eNB1 may not know how to combine a corresponding wideband CQI and differential sub-band CQI (with fewer than 16 possibilities) in order to obtain the full CQI for that subband, for instance, in the case that the precise feedback mode configured for the UE of interest under that CSI process is not conveyed to the receiving eNB1. We note here also that it might be desirable to not impose restrictions on sending eNB2 on how it combines reports from multiple different feedback modes configured for that UE under the same CSI process. Then, note that when aperiodic feedback mode 3-1 is configured for the UE (by eNB2), the UE reported sub band CQI is encoded differentially with respect to the corresponding wideband CQI using 2 bits representing differential values {−2, 0, 1, 2}. On the other hand, in the case of aperiodic feedback mode 2-0 or 2-2, only the best M-average is reported by the UE by differentially encoding it with respect to a corresponding wideband CQI using 2 bits representing differential values {1, 2, 3, 4}. Further, in case of periodic feedback mode 2-1 the CQI corresponding to codeword-1 for each UE selected subband within a bandwidth part can itself be of 4 bits, whereas that of codeword-2 (when RI>1) is differentially encoded with respect to CQI of codeword-1 using 3 bits.

It becomes apparent from the above discussion that a transparent way of conveying CQI (without having to convey all details regarding to one or more feedback modes configured under that CSI process for that UE) is to allow for full (complete) CQI for each indicated subband.

Another issue that is important, is to ensure that the RI and CQIs conveyed by eNB2 to eNB1 in a UE CSI report are mutually consistent, i.e., all the reported CQIs are computed by the UE for the same RI (which is identical to the one in the Rank Indication IE when the latter is present). This issue is important to address because under certain feedback modes (such as periodic mode 2-1) the RI and the wideband CQI(s) as well as the subband CQI(s) for one or more bandwidth portions can be reported by the UE on different subframes. Thus, depending on the periodicity defined by eNB1 in its CSI request, it can happen that the latest RI available for the UE under the CSI process, can be different from the one for which the most recent CQI(s) are computed. In such a case, the sending eNB2 should ensure that its CSI report is consistent, for instance by using the RI value for which the most recently available CQI(s) have been computed.

The variation (which allows the requesting eNB to specify whether or not it wants to receive subband CQI(s) or Rank Indication is provided below. In this context, we note that since the requesting eNB1 has no control over how eNB2 configures CSI processes (and constituent feedback modes) for its users, it should be in any case able to exploit different type of CSI reports (wideband only or wideband and subband).

TABLE D7 IE type and Semantics IE/Group Name Presence Range reference description CSI per UE 1 . . . <maxnoofUE- CSI> >C-RNTI M BIT STRING (SIZE (16)) >CSI per Interference 1 . . . Hypotheses <maxnoofInterferenceHypothesis> >>Interference Hypothesis M [FFS] Information >>Wideband CQI for M INTEGER(0 . . . Codeword 0 15, . . . ) >>Wideband CQI for O INTEGER(0 . . . Codeword 1 15, . . . ) >>Rank Indication O INTEGER(1 . . . The rank indication 8, . . . ) IE is present only if it is requested in the associated request. In that case it follows the definition in TS 36.213 [11]. >>Subband CQI List 0 . . . This IE is present <maxnoofSubband> only if associated request wants subband CQI. In that case subbands are listed in the order of increasing frequency. >>>Subband Start O INTEGER(0 . . . PRB number of the 109, . . .) first PRB in the subband. If this IE is not present, the subband is contiguous with the previous subband in the list, or starts with PRB 0 if this is the first subband in the list. >>>Subband Size O INTEGER(1 . . . Number of 110, . . . ) contiguous PRBs in the subband. If this IE is not present, the value is the same as the previous subband in the list. >>>Subband CQI for M INTEGER(0 . . . Codeword 0 15, . . . ) >>>Subband CQI for O INTEGER(0 . . . Codeword 1 15, . . . )

Another variation which allows for further simplification at the expense of not being bit efficient is as follows. Here the full CQIs for all possible subbands (which can be determined by the number of PRBs in the downlink available at eNB2) are always conveyed for a UE under the CSI process. In case the sub band CQI is not reported by a UE under the configured feedback mode for a subband, the sending eNB2 simply uses the wideband CQI value for that subband.

9.2.19 Relative Narrowband Tx Power (RNTP)

This IE provides an indication on DL power restriction per PRB in a cell and other information needed by a neighbour eNB for interference aware scheduling.

TABLE D8 IE/Group IE type and Semantics Assigned Name Presence Range reference description Criticality Criticality RNTP Per M BIT Each position in — — PRB STRING the bitmap (6 . . . 110, . . . ) represents a n_(PRB) value (i.e. first bit = PRB 0 and so on), for which the bit value represents RNTP (n_(PRB)), defined in TS 36.213 [11]. Value 0 indicates “Tx not exceeding RNTP threshold”. Value 1 indicates “no promise on the Tx power is given”. This IE is used to indicate DL power restriction per PRB for the first subframe. In case the DL power restriction is static, the indicated DL power restriction is maintained over the subsequent subframes. RNTP M ENUMERATED RNTP_(threshold) is — — Threshold (−∞, defined in TS −11, −10, −9, 36.213 [11]. −8, −7, −6, −5, −4, −3, −2, −1, 0, 1, 2, 3, . . . ) Number Of M ENUMERATED P (number of — — Cell-specific (1, 2, 4, . . . ) antenna ports Antenna for cell-specific Ports reference signals) defined in TS 36.211 [10] P_B M INTEGER P_(B) is defined in — — (0 . . . 3, . . . ) TS 36.213 [11]. PDCCH M INTEGER Measured by — — Interference (0 . . . 4, . . . ) Predicted Impact Number Of Occupied PDCCH OFDM Symbols (see TS 36.211 [10]). Value 0 means “no prediction is available”. Extended O BIT Each position in RNTP Per STRING the bitmap PRB (6 . . . 4290, . . . ) represents a PRB in a subframe, for which value “1” indicates ‘no promise on the Tx power is given’ and value “0” indicates ‘Tx not exceeding RNTP threshold.’ The first bit corresponds to PRB 0 of the first subframe for which the extended RNTP per PRB IE is valid, the second bit corresponds to PRB 1 of the first subframe for which the extended RNTP per PRB IE is valid, and so on. The length of the bit string is an integer (maximum 39) multiple of N_(RB) ^(DL) . N_(RB) ^(DL) is defined in TS 36.211 [10]. The bit string may span across multiple contiguous subframes. The pattern across contiguous subframes (formed by RNTP per PRB and extended RNTP per PRB) is continuously repeated. RNTP per 0 . . . 1 PRB start time >Starting M INTEGER SFN of the radio SFN (0 . . . 1023, . . . ) frame containing the first subframe when the RNTP Per PRB IE is valid. >Starting M INTEGER Subframe Subframe (0 . . . 9, . . . ) number, within Index the radio frame indicated by the Start SFN IE, of the first subframe when the RNTP Per PRB IE is valid.

An alternate Table for RNTP enhancement is given below.

TABLE D9 IE/Group IE type and Semantics Assigned Name Presence Range reference description Criticality Criticality RNTP per PRB M BIT Each position in — — STRING the bitmap (6 . . . 110, . . . ) represents a n_(PRB) value (i.e. first bit = PRB 0 and so on), for which the bit value represents RNTP (n_(PRB)), defined in TS 36.213 [11]. Value 0 indicates “Tx not exceeding RNTP threshold”. Value 1 indicates “no promise on the Tx power is given”. This IE is ignored if the RNTP per PRB per subframe IE is present. RNTP M ENUMERATED RNTP_(threshold) is — — Threshold (−∞, defined in TS −11, −10, −9, 36.213 [11]. −8, −7, −6, −5, −4, −3, −2, −1, 0, 1, 2, 3, . . . ) Number Of M ENUMERATED P (number of — — Cell-specific (1, 2, 4, . . . ) antenna ports Antenna Ports for cell-specific reference signals) defined in TS 36.211 [10] P_B M INTEGER P_(B) is defined in — — (0 . . . 3, . . . ) TS 36.213 [11]. PDCCH M INTEGER Measured by — — Interference (0 . . . 4, . . . ) Predicted Impact Number Of Occupied PDCCH OFDM Symbols (see TS 36.211 [10]). Value 0 means “no prediction is available”. RNTP Per O BIT Each position in PRB per STRING the bitmap subframe (6 . . . 4400, . . . ) represents a PRB in a subframe, for which value “1” indicates ‘no promise on the Tx power is given’ and value “0” indicates ‘Tx not exceeding RNTP threshold.’ The first bit corresponds to PRB 0 of the first subframe for which the RNTP per PRB per subframe IE is valid, the second bit corresponds to PRB 1 of the first subframe for which the RNTP per PRB per subframe IE is valid, and so on. The length of the bit string is an integer (maximum 40) multiple of N_(RB) ^(DL). N_(RB) ^(DL) is defined in TS 36.211 [10]. The bit string may span across multiple contiguous subframes. The pattern across contiguous subframes formed by RNTP per PRB per subframe IE is continuously repeated. RNTP per 0 . . . 1 PRB per subframe start time >Starting M INTEGER SFN of the radio SFN (0 . . . 1023, . . . ) frame containing the first subframe when the RNTP Per PRB Per Subframe IE is valid. >Starting M INTEGER Subframe Subframe (0 . . . 9, . . . ) number, within Index the radio frame indicated by the Start SFN IE, of the first subframe when the RNTP Per PRB Per Subframe IE is valid.

Another alternate Table for RNTP enhancement is given below.

TABLE D10 IE/Group IE type and Semantics Assigned Name Presence Range reference description Criticality Criticality RNTP per PRB M BIT Each position in — — STRING the bitmap (6 . . . 110, . . . ) represents a n_(PRB) value (i.e. first bit = PRB 0 and so on), for which the bit value represents RNTP (n_(PRB)), defined in TS 36.213 [11]. Value 0 indicates “Tx not exceeding RNTP threshold”. Value 1 indicates “no promise on the Tx power is given”. This IE is ignored if the RNTP per PRB per subframe IE is present. RNTP M ENUMERATED RNTP_(threshold) is — — Threshold (−∞, defined in TS −11, −10, −9, 36.213 [11]. −8, −7, −6, −5, −4, −3, −2, −1, 0, 1, 2, 3, . . . ) Number Of M ENUMERATED P (number of — — Cell-specific (1, 2, 4, . . . ) antenna ports Antenna Ports for cell-specific reference signals) defined in TS 36.211 [10] P_B M INTEGER P_(B) is defined in — — (0 . . . 3, . . . ) TS 36.213 [11]. PDCCH M INTEGER Measured by — — Interference (0 . . . 4, . . . ) Predicted Impact Number Of Occupied PDCCH OFDM Symbols (see TS 36.211 [10]). Value 0 means “no prediction is available”. RNTP Per O BIT Each position in PRB per STRING the bitmap subframe (6 . . . 4400, . . . ) represents a PRB in a subframe, for which value “1” indicates ‘resource with no utilization constraints’ and value “0” indicates ‘interference protected resource.’ The first bit corresponds to PRB 0 of the first subframe for which the RNTP per PRB per subframe IE is valid, the second bit corresponds to PRB 1 of the first subframe for which the RNTP per PRB per subframe IE is valid, and so on. The length of the bit string is an integer (maximum 40) multiple of N_(RB) ^(DL). N_(RB) ^(DL) is defined in TS 36.211 [10]. The bit string may span across multiple contiguous subframes. The pattern across contiguous subframes formed by RNTP per PRB per subframe IE is continuously repeated. RNTP per 0 . . . 1 PRB per subframe start time >Starting M INTEGER SFN of the radio SFN (0 . . . 1023, . . . ) frame containing the first subframe when the RNTP Per PRB Per Subframe IE is valid. >Starting M INTEGER Subframe Subframe (0 . . . 9, . . . ) number, within Index the radio frame indicated by the Start SFN IE, of the first subframe when the RNTP Per PRB Per Subframe IE is valid.

Another alternative using multiple thresholds conveyed via 2 bits is given below.

TABLE D11 IE/Group IE type and Semantics Assigned Name Presence Range reference description Criticality Criticality ERNTP Per M BIT Each position in — — PRB and STRING the bitmap subframe (12 . . . 220, . . .) represents a PRB in a subframe, for which the value “xx” indicates how the transmission power in a resource block is mapped relative to the two power thresholds: 00 - power level not exceeding the LPTH 01 - power level between LPTH and MPTH; 10 - power level between MPTH and HPTH; 11 - no promise on the Tx power is given. The first 2 bits correspond to PRB 0 of the first subframe for which the IE is valid, the following 2 bits correspond to PRB 1 of the first subframe for which the IE is valid, and so on. The bit string may span across multiple contiguous subframes. The length of the bit string is an integer (maximum 40) multiple of. The parameter is defined in TS 36.211 [10]. The ERNTP pattern is continuously repeated with a periodicity indicated in Periodicity. Transmitted power levels LPTH (Low M ENUMERATED Lower RNTP — — Power (−∞, −11, power Threshold) −10, −9, −8, threshold, using −7, −6, −5, −4, the −3, −2, −1, 0, RNTP_(threshold) 1, 2, 3, . . .) defined in TS 36.213 [11]. MPTH M ENUMERATED Medium RNTP (Medium (−∞, −11, power Power −10, −9, −8, threshold, using Threshold) −7, −6, −5, −4, the −3, −2, −1, 0, RNTP_(threshold) 1, 2, 3, . . .) defined in TS 36.213 [11]. HPTH (High M ENUMERATED Higher RNTP Power (−∞, −11, power Threshold) −10, −9, −8, threshold, using −7, −6, −5, −4, the RNTP_(threshold) −3, −2, −1, 0, defined in TS 1, 2, 3, . . .) 36.213 [11]. Subframe sequence definition >Start SFN M INTEGER SFN of the radio (0 . . . 1023) frame containing the first subframe where the RNTP Per PRB Per Subframe IE is valid. >Start M INTEGER Subframe Subframe (0 . . . 39) number, within Number the radio frame indicated by the Start SFN IE, of the first subframe when the RNTP Per PRB Per Subframe IE is valid. No. of M 1 . . . 40 No. of subframes subframes for which is defined the bitstream Periodicity 1 . . . 40 The number of subframes after which the bit pattern is repeated Number Of M ENUMERATED P (number of Cell-specific (1, 2, 4, . . .) antenna ports Antenna Ports for cell-specific reference signals) defined in TS 36.211 [10] P_B M INTEGER P_(B) is defined in (0 . . . 3, . . .) TS 36.213 [11].

The point in the table given above is that since the choice ‘11’ already indicates no promise on the power level (which covers the case of transmit power being arbitrarily high) we can use three thresholds (instead of two) since there is no need to convey that the power level is greater than HPTH (as this is subsumed by ‘11’).

However, one problem with indicating multiple thresholds is that the current CoMP hypothesis (implicitly) assumes just one threshold. In this sense there is a mismatch between using multiple thresholds in eRNTP and not in the CoMP hypothesis. Consequently, the full potential of multiple thresholds may not be realized inspire of the additional overhead.

Suppose that there are L subband selection types denoted by {(N₁, q₁), . . . , (N_(L), q_(L))}, where the l^(th) selection type is defined by N_(l), q_(l) which denote the total number of subbands and the number of subbands that must be selected, respectively, under that type. Note that under each selection type the size of each subband is fixed and known a-priori. Further, suppose that there are J bandwidth portions, each portion comprising S_(j), 1≦j≦J subbands. Only one subband is selected from the S_(j) subbands in each bandwidth portion jε{1, . . . , J}. Further since the user sequentially reports its CSI report for the bandwidth portions, we can impose a nested structure on the corresponding exchange of CSI from sending eNB2 to receiving eNB1. In particular, we impose the structure under which the CSI of any subband in the j^(th) portion is sent only if the CSI of a subband in each of the preceeding j−1 bandwidth portions are sent. This structure enables efficient exchange of CSI without any loss of generality. Thus, overall there are L+J different selection types possible (with the last J types associated with the selections from bandwidth portions). Then, each selection in the total number of distinct subband selections can be identified by a combinatorial index R whose range is given by

$0,\ldots \mspace{14mu},{{\sum_{j = 1}^{L}\begin{pmatrix} N_{j} \\ q_{j} \end{pmatrix}} + \left( {\sum_{j = 1}^{J}{\prod_{k = 1}^{j}S_{k}}} \right) - 1.}$

We next discuss the generation of the index at the sending eNB followed by the determination of the particular selection from the index at the receiving eNB. Towards this end, we define a set of offsets as follows:

${O_{l} = {O_{l - 1} + \begin{pmatrix} N_{l - 1} \\ q_{l - 1} \end{pmatrix}}},$

l=2, . . . , L+1 and O₁=0. Further, we set O_(l)=O_(l-1)+Π_(j=1) ^(l-L-1)S_(j), l=L+2, . . . , L+J.

Generation of Index at Sending eNB

-   -   At the sending eNB, first identify the selection type l.     -   If lε{1, . . . , L} then q_(l) subbands are selected from N_(l)         total subbands. Let m₀, . . . , m_(q) _(l) ₋₁ be the selected         subband indices that are ordered, i.e., m₀<m₁< . . . <m_(q) _(l)         ₋₁ and all lie in {1, . . . , N_(l)}. Set

$R = {O_{l} + {\sum_{j = 0}^{q_{l} - 1}{\begin{pmatrix} {N_{l} - m_{j}} \\ {q_{l} - j} \end{pmatrix}.}}}$

-   -   Else lε{L+1, . . . , L+J}. Let m₁, . . . , m_(l-L) denote the         chosen subband indices, one from each of the first l−L bandwidth         portions, and where m_(j)ε{1 . . . , S_(j)}, j=1, . . . l−L. Set         R=O_(l)+Π_(j=1) ^(l-L)m_(j)−1.

Retrieving Subband Selection from Index at Receiving eNB

-   -   At the receiving eNB, find the greatest l such that O_(l)≦R.     -   If lε{1, . . . , L} then q_(l) subbands have been selected from         N_(l) total subbands. Let m₀, . . . , m_(q) _(l) ₋₁ be the         ordered subband indices that need to be determined. Initialize         a=1, r=R−O_(l).     -   For k=0, . . . , q_(l)−1 Do     -   b=a,

$Q = {\begin{pmatrix} {N_{l} - b} \\ {q_{l} - k} \end{pmatrix}.}$

-   -   While Q>r Do: b=b+1 and

$Q = {\begin{pmatrix} {N_{l} - b} \\ {q_{l} - k} \end{pmatrix}\text{:}}$

EndWhile

-   -   m_(k)=b, a=b+1, r=r−Q.     -   Else lε{L+1, . . . , L+J}. Let m₁, . . . , m_(l-L) denote the         subband indices that need to be determined, one from each of the         first l−L bandwidth portions, and where m_(j)ε{1 . . . , S_(j)},         j=1, . . . l−L. Set r=R−O_(l), B=l−L and A=S₁× . . . ×S_(B).     -   For k=1, . . . , B−1 Do     -   A=A/S_(k),

$\hat{m} = \left\lfloor \frac{r}{A} \right\rfloor$

and m_(k)={circumflex over (m)}+1.

-   -   Update r=r−{circumflex over (m)}S_(k)     -   m_(B)=r+1

Embodiment E E1 Introduction

We summarize the 3 options for subband definition, and provide enhancements for them, together with an enhancement for eRNTP (enhanced Relative Narrowband Tx Power).

E2 Summary of Solutions

General notes:

-   -   All the following options allows eNB to“process” CQI (channel         quality indication) values (implementation based manner) before         sending over X2.     -   Some of the main differentiators between the options are:

1) Simplicity, if sending eNB implementation only sends “raw” CSI (Channel State Information)→Option A, C (albeit only with the respective enhancements)

2) Flexibility, if sending eNB implementation processes CSI (e.g. combines or merges overlapping Periodic and Aperiodic reports)→Option B, C

Option A: Subband Index+Report Type

TABLE E1 >>Subband 0 . . . CQI List <maxSubband> >>>Subband M 9.2.cc CQI >>>Subband O INTEGER Included in case Index (0 . . . 27, . . . ) of UE selected subband CQI reporting. >>> Report O ENUMERATED Included in case Type (periodic, of UE selected aperiodic, . . . ) subband CQI reporting.

Notes for Option A:

-   -   Primary Motivation: Allows serving eNB to send CSI reports over         X2 with as little processing as possible     -   Description: The subband partitioning is fixed, based on the         UE's CSI reporting configuration. The Report Type and Subtend         Index IEs are used by the receiving eNB to derive the subband         positions and their size and total number of subbands. The         latter information is also important since it will enable         receiving eNB to determine what the differential CQI conveyed         for that subband means. This is because in aperiodic mode 3-0         (or 3-1) and aperiodic mode 2-0 (or 2-2) the same differential         value can be mapped to different offsets, respectively. Thus,         the only way the receiving eNB1 can deduce the right offset         value to use is to utilize the fact that for the given system         bandwidth (or given total number of PRBs (physical resource         blocks) available at sending eNB2 (which is known or conveyed         separately to eNB1)) the number of sub bands for which CQIs are         reported is distinct under those two aperiodic modes,         respectively. Another alternative is to convey the exact         configured feedback mode (such as aperiodic 3-1 etc) under the         Report type IE (information element).     -   Allows sending “raw” CQI over X2, in a format similar to what is         received from the UE (i.e. Subband Index)     -   Allows sending both Periodic and Aperiodic reports in the same         X2 message; in case of overlapping Aperiodic and Periodic CSI         reports, the handling is left to receiving eNB implementation         (e.g. merge, discard, etc). We note that sending two reports in         the same message is beneficial since otherwise several reports         may need to be dropped by the sending eNB in order to comply         with the one report per X2 message constraint and the         periodicity configured for the X2 messages.

However, a problem in sending both aperiodic and periodic subband reports together in the same X2 message as per the aforementioned structure, is that the associated reference wideband reports that are used to compute them can be different. In particular, the wideband rank indicators (RIs) that are determined by the UE under the configured aperiodic mode and the configured periodic mode can be different. Similarly, the wideband CQIs determined by the UE under the configured periodic mode and the configured aperiodic mode can be different. Furthermore, each subband CQI determined under the aperiodic mode is reported by the UE (over PUSCH (physical uplink shared channel)) as a differential value with respect to the corresponding wideband CQI. For example, suppose aperiodic feedback mode 2-2 and periodic feedback mode 2-1 are configured. Then, under the aperiodic mode 2-2 the UE will report one wideband CQI (per codeword) as well as one subband CQI (per codeword) for the selected best-M feedback as a differential value (using 2 bits) with respect to the wideband CQI corresponding to that codeword. On the other hand, under the periodic 2-1 mode the UE will report (over PUCCH (physical uplink control channel)) one wideband CQI (per codeword), with the wideband CQI of the second codeword being reported as a differential value with respect to the wideband CQI of the first one. In addition the UE will report one subband CQI for the first codeword and the second CQI as a differential value with respect to the subband CQI of the first one.

Therefore it becomes clear that we need to have separate sets of RIs and wideband CQIs in the X2 message whenever that message contains both aperiodic and periodic subband reports. If such separate sets of wideband components are not included then the receiving eNB will use the same wideband RI or CQI(s) for both aperiodic and periodic information. This defeats the purpose of conveying separate aperiodic and periodic subband reports in the same X2 message.

We propose an optimized structure in the following as a remedy to this issue.

TABLE E2 IE type and Semantics IE/Group Name Presence Range reference description CSI Report per UE 1 . . . <maxUEReport> >UE ID M BIT STRING ID of the UE served (SIZE(16)) by the cell in eNB₂. >CSI Report per 1 . . . CSI Process <maxCSIProcess> >> Report type per 0 . . . 1 CSI process >>>Report Type M ENUMERATED (periodic, aperiodic, . . . ) >>>RI M INTEGER (1 . . . Defined in TS 8, . . . ) 36.213 [11]. >>>Wideband M 9.2.bb CQI >>>Subband 0 . . . CQI List <maxSubband> >>>>Subband M 9.2.cc CQI >>>>Subband INTEGER (0 . . . Included in the case Index 27, . . . ) of UE selected subband CQI reporting. Range bound Explanation maxUEReport Maximum number of UE measurement reports. Value is 128. maxCSIProcess Maximum number of CSI processes. The value is 4. maxSubband Maximum number of subbands. The value can be 14 or 15 or 16 or 17 or 18 or 28

The value of 15 for the maxSubband is computed as 14+1, where 14 is the number of subbands in an aperiodic mode 3-0 or 3-1 assuming 110 DL (downlink) RBs (resource blocks) and 1 other subband is for periodic mode 2-0 or 2-1 assuming subband report for one bandwidth portion is allowed in the X2 message. Similarly, values 16, 17, 18 are computed assuming subband report for 2, 3, 4 bandwidth portions, respectively, are allowed in the same X2 message.

The same problem identified above can also arise when the sending eNB sends two different reports (corresponding to a configured periodic mode or corresponding to a configured aperiodic mode). The presented optimized structure addresses even such cases since it allows for two reporting types per CSI process of each UE. Each one of those two reporting types can be both periodic or both aperiodic.

In this context, we note that the value of maxSubband equal to 28 arises when we allow for two aperiodic reports, for example 28=14+14, where 14 is the number of subbands in an aperiodic mode 3-0 or 3-1 assuming 110 DL RBs.

Moreover, to provide further flexibility the range of the “Report type per CSI process” can be increased from two to a larger value such as 3 or 4 or 5.

9.2.bb Wideband CQI

This IE indicates the Wideband CQI as defined in TS 36.213.

TABLE E3 IE Type and Semantics IE/Group Name Presence Range Reference Description Wideband absolute CQI M INTEGER Encoded in Codeword 0 (0 . . . 15, . . . ) TS 36.213 [11]. CHOICE Wideband CQI O Codeword 1 >Wideband absolute CQI M INTEGER Encoded in Codeword 1 (0 . . . 15, . . . ) TS 36.213 [11]. >Wideband differential M INTEGER Encoded in CQI Codeword 1 (0 . . . 7, . . . ) TS 36.213 [11].

9.2.cc Subband CQI

This IE indicates the Subband CQI as defined in TS 36.213.

TABLE E4 IE Type and IE/Group Name Presence Range Reference Semantics Description CHOICE Subband M CQI Codeword 0 >Subband M INTEGER (0 . . . Encoded in TS 36.213 [11]. absolute CQI 15, . . . ) Codeword 0 >Subband M INTEGER (0 . . . 3, . . . ) Encoded in TS 36.213 [11]. differential CQI Codeword 0 CHOICE Subband O CQI Codeword 1 >Subband M INTEGER (0 . . . Encoded in TS 36.213 [11]. absolute CQI 15, . . . ) Codeword 1 >Subband M INTEGER (0 . . . 7, . . . ) Encoded in TS 36.213 [11]. differential CQI Codeword 1 >Subband M INTEGER (0 . . . 3, . . . ) Encoded in TS 36.213 [11]. differential CQI Codeword 1

Other equivalent variations of the optimized structure are possible with the common theme being that a separate wideband component (comprising RI and wideband CQI(s)) is conveyed for the aperiodic and the periodic reports, respectively, and where the structure should allow the receiving eNB to unambiguously associate the periodic and aperiodic subband components with their respective wideband counterparts. Notice that under the optimized structure if only one of the aperiodic or periodic subband information is reported in the X2 message, it will include only the corresponding wideband information.

Notice also that under the aperiodic feedback modes (2-0 and 2-1) the UE reports common subband information for all the best-M subbands, thus in the structure presented above the sender eNB will repeat the same subband CQI for all the best-M indicated subbands. This repetition can be avoided by modifying the structure as follows.

The subband CQI IE is made optional with the understanding that if this IE is not present the CQI for that subband is taken to be the same as that of the subband (closest to it in frequency and of the same reporting type) with a lower index for which the CQI has been conveyed in that message, with the restriction that the latter CQI must have been indicated.

Option B: Subband Start+Subband Size

TABLE E5 >>Subband CQI List 0 . . . <maxSubband> >>>Subband CQI M 9.2.cc >>>Subband Start O INTEGER Corresponds to the PRB (2 . . . 109, . . . ) number of the first PRB in a subband defined in TS 36.213 [11] for the system bandwidth.lf this IE is not present, the subband is contiguous with the previous subband in the list, or starts with PRB 0 if this is the first subband in the list. >>>Subband Size M ENUMERATED Corresponds to a value of (2, 3, 4, 6, 8, . . . ) subband size k defined in TS 36.213 [11] for the system bandwidth. Ignored for the highest frequency subband.

Notes for Option B:

-   -   Primary Motivation: Enables greater implementation flexibility         for sending “processed” CQI in alignment with the RAN3 agreement         that “the serving eNB can process CSI (implementation)”,         particularly for the case where UE is configured for both         Aperiodic and Periodic CSI reporting     -   Description: The Subband Start and Subband Size IEs are used to         explicitly indicate the subbands. The subbands are restricted to         those defined for the system bandwidth N_(RB) ^(DL).     -   Allows sending “raw” CQI over X2, but in a different format than         used by the UE (i.e. Subband Start)     -   Allows sending both Periodic and Aperiodic reports in the same         X2 message; in case of overlapping Aperiodic and Periodic CSI         reports, the sending eNB can process (e.g. merge) according to         implementation-specific algorithms

We note that in this structure given for option-B since only one set of wideband components are included, the sending eNB must harmonize RIs and wideband CQIs that are received from a periodic and aperiodic reports or two different periodic reports or two different aperiodic reports, respectively. In this context, using absolute value for the subband CQIs is particularly beneficial since then such CQIs can be directly used without matching them to any sideband reference.

As another optimization in this structure the Subband CQI IE can be made optional in which case the CQI for this subband is assumed to be the same as that of the last preceding subband for which a CQI is indicated. The CQI for the first sub band is always indicated. This optimization helps to avoid redundancies that can arise for instance in conveying best-M feedback as described before.

We note that here maximum number of subbands can be 28 (assuming 110 DL RBs and subband size of 4 under aperiodic mode 2-0 or 2-2).

Option C: Subband Index+Subband Size

TABLE E6 >>Subband 0 . . . CQI List <maxSubband> >>>Subband M 9.2.cc CQI >>>Subband O INTEGER Included in case of Index (0 . . . 27, . . . ) UE selected subband CQI reporting. >>>Subband M ENUMER - Corresponds to a Size ATED value of subband (2, 3, 4, 6, size k defined in TS 8, . . . ) 36.213 [11] for the system bandwidth. Ignored if the Subband Index corresponds to the highest frequency subband.

Notes for Option C:

-   -   Description: The Subband Size IE is used by sending eNB to         explicitly indicate the subband partitioning (rather than         receiving eNB deriving the subband partitioning based on         information about the UE's CSI reporting configuration). The PRB         number of the first PRB in the subband is calculated as (Subband         Index×Subband Size).

Allows sending “raw” CQI over X2, in a format similar to what is received from the UE (i.e. Subband Index)

Allows sending both Periodic and Aperiodic reports in the same X2 message; in case of overlapping Aperiodic and Periodic CSI reports, the sending eNB can process (e.g. merge) according to implementation-specific algorithms

If overlapping Aperiodic and Periodic CSI reports are received, then sending eNB can (as implementation option) “split” the Periodic subband into two Aperiodic subbands over X2. Assumption is that, according to subband definitions in TS 36.213, a Periodic subband is always composed of two Aperiodic subbands.

Example

N_(RB) ^(DL) is 50, and eNB receives two CSI reports over Uu during a given interval: Aperiodic Mode 2-* for subband index 1 (subband size 3) and Periodic Mode 2-* for subband index 0 (subband size 6). Then, eNB has several options for sending the information over X2:

a) Send both reports over X2 and let receiving eNB decide how to handle

b) Select one of the two reports to send over X2 (e.g. the latest report)

c) Merge the Aperiodic and Periodic reports into two Aperiodic reports over X2 (subband index 0 and 1)

The observation made in option-A regarding the need to send separate wideband components in case both aperiodic and periodic reports are sent on the same X2 message also holds in this case.

Thus, we need to modify option-C as the following:

TABLE E7 IE type and Semantics IE/Group Name Presence Range reference description CSI Report per UE 1 . . . <maxUEReport> >UE ID M BIT STRING ID of the UE served (SIZE(16)) by the cell in eNB₂. >CSI Report per CSI 1 . . . Process <maxCSIProcess> >> Refence type per 0 . . . 1 CSI process >>>Reference Type M ENUMERATED (periodic, aperiodic, . . . ) >>>RI M INTEGER (1 . . . Defined in TS 8, . . . ) 36.213 [11]. >>>Wideband CQI M 9.2.bb >>Subband CQI List 0 . . . <maxSubband> >>>Subband CQI M 9.2.cc >>>Subband Index O INTEGER Included in case of (0 . . . 27, . . . ) UE selected subband CQI reporting. >>>Subband Size M ENUMERATED Corresponds to a (2, 3, 4, 6, value of subband 8, . . . ) size k defined in TS 36.213 [11] for the system bandwidth. Ignored if the Subband Index corresponds to the highest frequency subband.

Other equivalent variations of the optimized structure are possible with the common theme being that a separate wideband component (comprising RI and wideband CQI(s)) is conveyed as a reference for the aperiodic and the periodic subband reports, respectively, and where the structure should allow the receiving eNB to unambiguously associate the periodic and aperiodic subband components with their respective wideband counterparts. Notice that under the optimized structure if only one of the aperiodic or periodic subband information is reported in the X2 message, it will include only the corresponding wideband information. Further, in case the structure includes merged CSI (where the merging or processing is done by the sender) then only one wideband component will be included and in this case all the subband CQIs will be conveyed as absolute CQIs (using 4 bits or 16 possibilities).

In this option the sending eNB must ensure that it uses the right number of subbands in its message when conveying the aperiodic CSI information. As described for option-A, doing so is important since it will enable receiving eNB to determine what the differential CQI conveyed for that subband means. This is because in aperiodic mode 3-0 (or 3-1) and aperiodic mode 2-0 (or 2-2) the same differential value can be mapped to different offsets, respectively. Thus, the only way the receiving eNB1 can deduce the right offset value to use is to utilize the fact that for the given system bandwidth (or given total number of PRBs available at sending eNB2 (which is known or conveyed separately to eNB1)) the number of sub bands for which CQIs are reported is distinct under those two aperiodic modes, respectively.

Option C′: Subband Index+Subband Size

TABLE E8 >>Subband M ENUMERATED Corresponds to a Size (2, 3, 4, 6, value of subband 8, . . . ) size k defined in TS 36.213 [11] for the system bandwidth. >>Subband 0 . . . CQI List <maxSubband> >>>Subband M 9.2.cc CQI >>>Subband O INTEGER Included in case of Index (0 . . . 27, . . . ) UE selected subband CQI reporting.

Notes for Option C′:

-   -   Description: Like Option C, but the Subband Size is fixed for         all subbands. Here maximum number of subbands can be 28         (assuming 110 DL RBs and subband size of 4 under aperiodic mode         2-0 or 2-2).

eRNTP Enhancements.

We provide an eRNTP version which allows the sender eNB to seamlessly convey either explicitly convey the applied power level (relative to one or more specified thresholds) or to convey whether a resource will be interference protected or not. We note that a resource can be interference protected by multiple methods which include lower power or by using an appropriate beam forming vector etc.

TABLE E9 IE type and Semantics Assigned IE/Group Name Presence Range reference description Criticality Criticality RNTP per PRB M BIT Each position in — — STRING the bitmap (6 . . . 110, . . .) represents a n_(PRB) value (i.e. first bit = PRB 0 and so on), for which the bit value represents RNTP (n_(PRB)), defined in TS 36.213 [11]. Value 0 indicates “Tx not exceeding RNTP threshold”. Value 1 indicates “no promise on the Tx power is given”. This IE is ignored if the Enhanced RNTP IE is present. RNTP Threshold O ENUMERATED RNTP_(threshold) is — — (−∞, −11, defined in TS −10, −9, −8, 36.213 [11]. This −7, −6, −5, −4, IE is always −3, −2, −1, 0, present if the 1, 2, 3, . . .) Enhanced RNTP IE is not present. Number Of M ENUMERATED P (number of — — Cell-specific (1, 2, 4, . . .) antenna ports for Antenna Ports cell-specific reference signals) defined in TS 36.211 [10] P_B M INTEGER P_(B) is defined in — — (0 . . . 3, . . .) TS 36.213 [11]. PDCCH M INTEGER Measured by — — Interference (0 . . . 4, . . .) Predicted Impact Number Of Occupied PDCCH OFDM Symbols (see TS 36.211 [10]). Value 0 means “no prediction is available”. Enhanced RNTP O BIT Each position in IE STRING the bitmap (6 . . . 4400, . . .) represents a PRB in a subframe. If the RNTP Threshold IE is present then the value “1” indicates ‘no promise on the Tx power is given’ and value “0” indicates ‘Tx not exceeding RNTP threshold.’ If the RNTP Threshold IE is not present then value “1” indicates ‘resource with no utilization constraints’ and value “0” indicates ‘interference protected resource.’ The first bit corresponds to PRB 0 of the first subframe for which the Enhanced RNTP IE is valid, the second bit corresponds to PRB 1 of the first subframe for which the Enhanced RNTP IE is valid, and so on. The length of the bit string is an integer (maximum 40) multiple of N_(RB) ^(DL). N_(RB) ^(DL) is defined in TS 36.211 [10]. The bit string may span across multiple contiguous subframes. The pattern across contiguous subframes formed by Enhanced RNTP IE is continuously repeated. Enhanced 0 . . . 1 RNTP IE start time >Starting SFN M INTEGER SFN of the radio (0 . . . 1023, . . .) frame containing the first subframe when the Enhanced RNTP IE is valid. >Starting M INTEGER Subframe number, Subframe Index (0 . . . 9, . . .) within the radio frame indicated by the Start SFN IE, of the first subframe when the Enhanced RNTP IE is valid.

Embodiment F F1. Introduction

In this document we discuss some issues with subband indexing schemes and then present our preference in a proposal.

F2. Discussion

F2.1 Conveying Both Periodic and Aperiodic Reports

A desirable feature that should be supported by a CSI signaling scheme is the exchange of both periodic and aperiodic CSI reports in the same X2 message, possibly in a combined (or merged) form. In the absence of this feature, i.e., when the sending eNB is forced to choose either the periodic or the aperiodic CSI report obtained under a CSI process of some user, the sending eNB will have to drop available CSI reports. This would be unfortunate given that precious over-the-air signaling resources have already been spent in acquiring these reports and these reports can together convey more CSI that either individual one.

Then, a problem that needs to be overcome in order to send both aperiodic and periodic subband reports together in the same X2 message, is described next. In particular, the associated reference wideband reports that are used to compute the constituent subband parts of the aperiodic and periodic CSI reports, respectively, can be different. Indeed, the wideband rank indicators (RIs) that are determined by the UE under the configured aperiodic mode and the configured periodic mode can be different. Similarly, the wideband CQIs determined by the UE under the configured periodic mode and the configured aperiodic mode are also more likely to be different. Furthermore, each subband CQI determined by the UE under the configured mode can be reported by it as a differential value with respect to a corresponding reference CQI. For example, suppose aperiodic feedback mode 2-2 and periodic feedback mode 2-1 are configured. Then, under the aperiodic mode 2-2 the UE will report (over PUSCH) one wideband CQI (per codeword) as well as one subband CQI (per codeword) for the selected best-M feedback as a differential value (using 2 bits) with respect to the wideband CQI corresponding to that codeword. On the other hand, under the periodic 2-1 mode the UE will report (over PUCCH) one wideband CQI (per codeword), with the wideband CQI of the second codeword being reported as a differential value with respect to the wideband CQI of the first one. In addition the UE will report one subband CQI for the first codeword and the second codeword subband CQI as a differential value with respect to the subband CQI of the first one.

Therefore it becomes clear that we have to alternatives to overcome this issue:

Alternative-1: Provision to include

two separate sets of RIs and wideband CQIs in the X2 message whenever that message contains both aperiodic and periodic subband reports. This will allow simple forwarding of both aperiodic and periodic reports in the same X2 message. In this context, we note that a structure which does not provide for including two separate sets of wideband components, forces the sending eNB to merge the wideband components and use a common reference for both aperiodic and periodic subband information. This defeats the purpose of conveying separate aperiodic and periodic subband reports in the same X2 message. Another issue in including the report type IE (specifying periodic or aperiodic report) within the list of subbands, is that ambiguity can be introduced when certain aperiodic and periodic reports are combined.

Alternative-2: Always merge separate sets of wideband components into one wideband component that will also be used as a common reference. In this case it is logical to merge the respective subband information as well, and upon doing so there is no need to indicate the type of the subband CSI report. However, this view prevents simple forwarding of both aperiodic and periodic reports in the same X2 message.

In order to obtain the merits of both the aforementioned alternatives, we propose a simple structure. This structure is presented in three versions, with the second and third ones being more bit-efficient version of the first.

The benefits of this proposal are as follows:

It allows for simple forwarding of both aperiodic and periodic reports in the same X2 message. In fact it allows for forwarding of multiple aggregated aperiodic or periodic CSI reports (from a UE under a CSI process) or their combinations in the same X2 message.

The parameter N_(RB) ^(DL) together with the conveyed subband size IE defines the subband partition, which corresponds to one of those defined in TS36.213.

It also allows for merging an aperiodic and a periodic report (or merging combinations of multiple periodic and/or multiple aperiodic CSI reports) without introducing any new subband definitions. This is because for a given total number of RBs (or PRBs), N_(RB) ^(DL), the subband size in aperiodic mode 2-* is exactly half of that of the aperiodic mode 3-* as well as periodic mode 2-*. Thus, in order to combine such reports we can use the subbands defined by the smaller subband size and convey (possibly processed) CQIs for them.

Other implementation based processing of the short-term CSI is also supported.

The first version is relatively straightforward. Two of its features are however worth pointing out:

For each CSI process we can convey up-to maxReferenceType reports. The Reference Type IE can be ENUMERATED for instance as periodic or aperiodic. Alternatively, the Reference Type IE can simply be dropped.

The subband CQIs are conveyed sequentially in the increasing order of subband indices. Then, in case the subband CQI IE for a subband is not conveyed, the receiving eNB must use the CQI conveyed for the last preceding subband. The CQI for the first subband must always be included. This feature can significantly save overhead by avoiding redundancy. Note that when a UE is configured in the aperiodic mode 2-*, it selects and reports indices for M out of N subbands. However, only one CQI (per codeword) is reported by it for all the M selected subbands. Therefore, it is beneficial that redundancy is avoided in reporting such CQIs.

The Subband Index IE is optional. In case this IE is not included then the subband CQI information for each one of the total number of subbands is conveyed. Recall that the parameter N_(RB) ^(DL) together with the conveyed subband size IE defines the subband partition, thereby conveying the total number of subbands N.

We now consider a more bit efficient second version in which the sub band selection is conveyed by means of a combinatorial index.

Here, under each Reference Type IE, the parameter N_(RB) ^(DL) together with the conveyed subband size IE defines the subband partition, thereby conveying the total number of subbands N. Also the number of subbands for which subband CQI is conveyed, M, is determined by the size of the Subband CQI List IE.

The combinatorial index, r, is defined based on TS36.213 (section 7.2.1) as follows:

The positions of the M selected subbands is conveyed using a combinatorial index r defined as

$r = {\sum\limits_{i = 0}^{M - 1}{\langle\begin{matrix} {N - s_{i}} \\ {M - i} \end{matrix}\rangle}}$

where N denotes the total number of subbands and the set {s_(i)}_(i=0) ^(M-1), (1≦s_(i)≦N, s_(i)<s_(i+1)) contains the M sorted subband indices and

${\langle\begin{matrix} x \\ y \end{matrix}\rangle} = \left\{ \begin{matrix} \begin{pmatrix} x \\ y \end{pmatrix} & {x \geq y} \\ 0 & {x < y} \end{matrix} \right.$

is the extended binomial coefficient, resulting in unique label

$r \in {\left\{ {0,\ldots \mspace{14mu},{\begin{pmatrix} N \\ M \end{pmatrix} - 1}} \right\}.}$

To illustrate, consider first the case when N_(RB) ^(DL)=110 and the Reference Type IE is set to be aperiodic. Then, we have two possibilities for subband selection. The first one is when the configured mode is 2-* in which case the subband size is 4 so that N=28 and here M=6. On the other hand, for aperiodic mode 3-* the subband size is 8 so that N=14 and here M=14. Similar argument applies to all other modes as well. It is also apparent that there is significant flexibility in aggregating several different reports under a Reference Type, as long as the subband partition is a valid one, i.e., corresponds to a one defined in TS36.213. Since the maximum value of N=28 (when N_(RB) ^(DL)=110 and subband size is 4) we represent the combinatorial index using a bit string of length 26. This allows us to convey any possible selection choice of subbands from the maximum of 28 subbands.

Next, we consider the third version in which the sub band selection is again conveyed by means of a combinatorial index. This version can be somewhat more restrictive compared to the second version but can also be more bit efficient. Here, the number of selected subbands and their size, in addition to their positions or indices, are also indicated by the combinatorial index.

Consider first the case when the Report Type IE is set to be aperiodic. Then, we have two possibilities for subband selection. The first one is when the configured mode is 2-* in which case the combinatorial index, r, is defined based on TS36.213 (section 7.2.1) as follows:

The positions of the M UE selected subbands is conveyed using a combinatorial index r defined as

$r = {\sum\limits_{i = 0}^{M - 1}{\langle\begin{matrix} {N - s_{i}} \\ {M - i} \end{matrix}\rangle}}$

where N denotes the number of subbands and the set {s_(i)}_(i=0) ^(M-1), (1≦s_(i)≦N, s_(i)<s_(i+1)) contains the M sorted subband indices and

${\langle\begin{matrix} x \\ y \end{matrix}\rangle} = \left\{ \begin{matrix} \begin{pmatrix} x \\ y \end{pmatrix} & {x \geq y} \\ 0 & {x < y} \end{matrix} \right.$

is the extended binomial coefficient, resulting in unique label

$r \in {\left\{ {0,\ldots \mspace{14mu},{\begin{pmatrix} N \\ M \end{pmatrix} - 1}} \right\}.}$

One additional possibility must be included to cover the case when the configured mode is 3-* in which case CQIs for all subbands have to be conveyed. We can choose r=−1 for this purpose. Then, notice that the combinatorial index, r, along with the parameter, N_(RB) ^(DL), together convey the total number of subbands, N, and the number of selected subbands, M, as well as the size of each subband and their positions or indices.

Consider next the case when the Report Type IE is set to be periodic. We consider the mode 2-* that is the only mode under which the subband information is reported. Here the user reports CSI for one selected subband from each one of the J bandwidth parts (or portions) sequentially over successive reporting instances. Therefore, depending on the periodicities configured for the X2 CSI exchange and the over-the-air reports, the sending eNB can have subband reports for up-to J subbands. Notice that since the user must report the information for each subband sequentially, no bandwidth part indicator is defined in TS36.213. We adopt the same approach and enforce that the subband CSI for all available bandwidth parts must be reported in the same X2 message. This nested structure will make the X2 message self-contained and avoid the need for a separate bandwidth part indicator.

Accordingly, letting N1, N2, . . . , NJ, denote the number of subbands in each of the J bandwidth parts, the combinatorial index must cover for N1 possibilities for the subband selection from the first bandwidth part, N1*N2 possibilities for the subband selections together from the first and second bandwidth parts, and so on till N1*N2* . . . NJ possibilities for the subband selections together from all the J bandwidth parts.

F3. Conclusion

We discussed the necessary X2 message to support CSI exchange for inter-eNB CoMP and presented our views on subband indexing along with corresponding proposals.

9.1.2.14 RESOURCE STATUS UPDATE

This message is sent by eNB₂ to neighbouring eNB₁ to report the results of the requested measurements.

Direction: eNB₂→eNB₁.

9.2.aa UE-CSI Report (Version-1)

This IE provides UE-CSI information for a set of UEs served by eNB₂.

TABLE F1 IE type and Semantics IE/Group Name Presence Range reference description CSI Report per UE 1 . . . <maxUEReport> >UE ID M BIT STRING ID of the UE (SIZE(16)) served by the cell in eNB₂. >CSI Report per CSI 1 . . . Process <maxCSIProcess> >> UE-CSI process M FFS FFS CSI process Configuration index configuration information. >> Reference type per 1 . . . CSI process <maxReferenceTypes> >>>Reference Type M ENUMERATED >>>RI M INTEGER (1 . . . Defined in TS 8, . . . ) 36.213 [11]. >>>Wideband CQI M 9.2.bb >>> Subband Size M ENUMERATED Corresponds to a (2, 3, 4, 6, value of subband 8, . . . ) size k defined in TS 36.213 [11] for the system bandwidth. Ignored if the Subband Index corresponds to the highest frequency subband. >>>Subband CQI List 1 . . . <maxSubband> >>>>Subband CQI O 9.2.cc If this IE is not present, the CQI is identical to the one provided for the last preceding subband. This IE is always present for the first subband in the list. >>>>Subband Index O INTEGER (0 . . . 27, . . . ) Range bound Explanation maxUEReport Maximum number of UE measurement reports. Value is 128. maxCSIProcess Maximum number of CSI processes. The value is 4. maxReferenceTypes Maximum types of of CSI reports. The value is 2. maxSubband Maximum number of subbands. The value is 28

Alternatively, the value of maxReferenceTypes can be 3 or 4.

UE-CSI Report (Version-2)

TABLE F2 IE type and Semantics IE/Group Name Presence Range reference description CSI Report per UE 1 . . . <maxUEReport> >UE ID M BIT STRING ID of the UE (SIZE(16)) served by the cell in eNB₂. >CSI Report per CSI 1 . . . Process <maxCSIProcess> >> UE-CSI process M FFS FFS CSI process Configuration index configuration information. >> Reference type 1 . . . per CSI process <maxReferenceTypes> >>>Reference Type M ENUMERATED >>>RI M INTEGER (1 . . . Defined in TS 8, . . . ) 36.213 [11]. >>>Wideband CQI M 9.2.bb >>> Subband Size M ENUMERATED Corresponds to a (2, 3, 4, 6, value of subband 8, . . . ) size k defined in TS 36.213 [11] for the system bandwidth. Ignored if the Subband Index corresponds to the highest frequency subband. >>> combinatorial M BITSTRING As defined in index (SIZE(26)) TS36.213 (section 7.2.1). The indices of the subbands in the list are indicated by this combinatorial index. Subband CQIs are sorted in the order of increasing frequency (increasing subband indices). >>>Subband CQI List 1 . . . <maxSubband> >>>>Subband CQI 0 9.2.cc If this IE is not present, the CQI is identical to the one provided for the last preceding subband. This IE is always present for the first subband in the list. Range bound Explanation maxUEReport Maximum number of UE measurement reports. Value is 128. maxCSIProcess Maximum number of CSI processes. The value is 4. maxReferenceTypes Maximum types of of CSI reports. The value is 2. maxSubband Maximum number of subbands. The value is 28

Version-3:

TABLE F3 IE type and Semantics IE/Group Name Presence Range reference description CSI Report per UE 1 . . . <maxUEReport> >UE ID M BIT STRING ID of the UE (SIZE(16)) served by the cell in eNB₂. >CSI Report per CSI 1 . . . Process <maxCSIProcess> >>UE-CSI process M FFS FFS CSI process Configuration index configuration information. >> Reference type per 1 . . . CSI process <maxReferenceTypes> >>>Reference Type M ENUMER- ATED >>>RI M INTEGER Defined in TS (1 . . . 8, . . . ) 36.213 [11]. >>>Wideband CQI M 9.2.bb >>> combinatorial index M As defined in TS36.213 (section 7.2.1). The number of subbands in the list, their indices, as well their size, are indicated by this combinatorial index. Subband CQIs are sorted in the order of increasing frequency (increasing subband indices). >>>Subband CQI List 1 . . . <maxSubband> >>>>Subband CQI O 9.2.cc If this IE is not present, the CQI is identical to the one provided for the last preceding subband. This IE is always present for the first subband in the list. Range bound Explanation maxUEReport Maximum number of UE measurement reports. Value is 128. maxCSIProcess Maximum number of CSI processes. The value is 4. maxReferenceTypes Maximum types of of CSI reports. The value is 2. maxSubband Maximum number of subbands. The value is 28

Embodiment G G1. Introduction

In order to meet the objectives of the Inter eNB CoMP WI it was agreed to extend the RNTP IE to include transmission power level indication per time frequency resources spanning across multiple subframes.

In the following, we provide our views on content of this message, as well as proposals.

G2. Discussion

G2.1 eRNTP Exchange

One concern that was raised during the discussions in RAN3#87bis was on the semantic description of the enhanced RNTP IE whether it is suitable to use the phrase “TX power not exceeding a threshold”. This is because certain implementations can achieve “interference protection” via other means such as beam-forming or beam-steering. We believe that even for such implementations, there is a notion of a threshold on effective radiated power from which the receiving eNB can deduce if a resource would be interference protected or not. We note that effective radiated power is a commonly used metric (terminology) which captures the effect of several relevant parameters such as transmit power, antenna gain, directivity, etc. Consequently, it is suitable to have an explicit threshold associated with the enhanced RNTP which indicates the “action” by the sender. We note that it is possible for sender eNB to send different eRNTP messages to different receiving eNBs to convey the potentially different net impacts of its adopted beam patterns and transmit powers on those receiving eNBs.

Accordingly, our preference is to retain the baseline agreement from the last meeting with a modification in the semantic description to use the phrase “Effective radiated TX power” instead of “TX power”. This will also accommodate newer implementations that rely on spatial/antenna domain processing to achieve interference mitigation.

We present two proposals. The first one is a more bit-efficient version of the BL agreement (albeit including the aforementioned modified semantic description). It exploits that fact an RNTP IE indicating transmit power levels for the first subframe (subframe #0) must always conveyed. Then, instead of ignoring this IE in the case when the enhanced RNTP IE is included, we can still use it to convey the per-PRB power level information for the first subframe. Moreover, instead of providing per-PRB power level information for each subsequent subframe in the enhanced RNTP IE, we can optionally adopt a more efficient representation in which such information for a subframe is conveyed only if it differs from that of the preceding one.

The second proposal is based on multiple thresholds, where we note that certain implementation can extract gains from such finer power level indication. The point here is that since the choice ‘11’ already indicates no promise on the effective radiated transmit power level (which covers the case of transmit power being arbitrarily high) we can use three thresholds (instead of two), since there is no need to convey that the power level is greater than HPTH (as this is subsumed by ‘11’).

G3. Conclusion

We discussed the necessary X2 message to support eRNTP exchange for inter-eNB CoMP and presented corresponding proposals.

Proposal:

9.2.19 Relative Narrowband Tx Power (RNTP)

This IE provides an indication on DL power restriction per PRB in a cell and other information needed by a neighbour eNB for interference aware scheduling.

TABLE G1 IE type and IE/Group Name Presence Range reference Semantics description RNTP Per PRB M BIT STRING Each position in the bitmap (6 . . . 110, . . . ) represents a n_(PRB) value (i.e. first bit = PRB 0 and so on), for which the bit value represents RNTP (n_(PRB)), defined in TS 36.213 [11]. Value 0 indicates “Effective radiated Tx power not exceeding RNTP threshold”. Value 1 indicates “no promise on the Effective radiated Tx power is given”. This IE is used to indicate DL power restriction per PRB for the first subframe. RNTP Threshold M ENUMERATED RNTP_(threshold) is defined in (−∞, −11, −10, −9, −8, TS 36.213 [11]. −7, −6, −5, −4, −3, −2, −1, 0, 1, 2, 3, . . . ) Number Of M ENUMERATED (1, P (number of antenna ports Cell-specific 2, 4, . . . ) for cell-specific reference Antenna Ports signals) defined in TS 36.211 [10] P_B M INTEGER (0 . . . 3, . . . ) P_(B) is defined in TS 36.213 [11]. PDCCH M INTEGER (0 . . . 4, . . . ) Measured by Predicted Interference Number Of Occupied Impact PDCCH OFDM Symbols (see TS 36.211 [10]). Value 0 means “no prediction is available”. Enhanced O BIT STRING Each position in the bitmap RNTP (6 . . . 4290, . . . ) represents a PRB in a subframe, for which value “1” indicates ‘no promise on the Effective radiated Tx power is given’ and value “0” indicates Effective radiated Tx power not exceeding RNTP threshold.’ The first bit corresponds to PRB 0 of the first subframe for which the IE is valid, the second bit corresponds to PRB 1 of the first subframe for which the IE is valid, and so on. The length of the bit string is an integer (maximum 39) multiple of N_(RB) ^(DL) which is defined in TS 36.211 [10]. The bit string may span across multiple contiguous subframes. The pattern across contiguous subframes (formed by RNTP IE and Enhanced RNTP IE) is continuously repeated

TABLE G2 IE/Group IE type and Semantics Assigned Name Presence Range reference description Criticality Criticality RNTP Per PRB M BIT Each position in — — STRING the bitmap (6 . . . 110, . . .) represents a n_(PRB) value (i.e. first bit = PRB 0 and so on), for which the bit value represents RNTP (n_(PRB)), defined in TS 36.213 [11]. Value 0 indicates “Effective radiated Tx power not exceeding RNTP threshold”. Value 1 indicates “no promise on the Effective radiated Tx power is given”. This IE is ignored when the enhanced RNTP IE is included. RNTP M ENUMERATED RNTP_(threshold) is — — Threshold (−∞, −11, defined in TS −10, −9, −8, 36.213 −7, −6, −5, −4, [11]. This IE is −3, −2, −1, 0, ignored when 1, 2, 3, . . .) the enhanced RNTP IE is included. Number Of M ENUMERATED P (number of — — Cell-specific (1, 2, 4, . . .) antenna ports for Antenna Ports cell-specific reference signals) defined in TS 36.211 [10] PDCCH M INTEGER Measured by — — Interference (0 . . . 4, . . .) Predicted Impact Number Of Occupied PDCCH OFDM Symbols (see TS 36.211 [10]). Value 0 means “no prediction is available”. Enhanced O BIT Each position — — RNTP STRING in the bitmap (12, . . . 8800, . . .) represents a PRB in a subframe, for which the value “xx” indicates how the Effective radiated transmission power in a resource block is mapped relative to the three power thresholds: 00 - Effective radiated TX power level not exceeding the LPTH 01 - Effective radiated TX power level between LPTH and MPTH; 10 - Effective radiated TX power level between MPTH and HPTH: 11 - no promise on the Effective radiated TX power is given. The first 2 bits correspond to PRB 0 of the first subframe for which the IE is valid, the following 2 bits correspond to PRB 1 of the first subframe for which the IE is valid, and so on. The bit string may span across multiple contiguous subframes. The length of the bit string is an integer (maximum 40) multiple of, N_(RB) ^(DL) which is defined in TS 36.211 [10]. The Enhanced RNTP pattern is continuously repeated > Enhanced RNTP thresholds >>LPTH (Low M ENUMERATED Lower RNTP — — Power (−∞, −11, power Threshold) −10, −9, −8, threshold, −7, −6, −5, −4, using the −3, −2, −1, 0, RNTP_(threshold) 1, 2, 3, . . .) defined in TS 36.213 [11]. >>MPTH M ENUMERATED Medium RNTP (Medium (−∞,−11, power Power −10, −9, −8, threshold, Threshold) −7, −6, −5, −4, using the −3, −2, −1, 0, RNTP_(threshold) 1, 2, 3, . . .) defined in TS 36.213 [11]. >>HPTH M ENUMERATED Higher RNTP (High Power (−∞, −11, power Threshold) −10, −9, −8, threshold, −7, −6, −5, −4, using the −3, −2, −1, 0, RNTP_(threshold) 1, 2, 3, . . .) defined in TS 36.213 [11].

Alternative structure for subband indexing:

TABLE G3 IE type and Semantics IE/Group Name Presence Range reference description CSI Report per UE 1 . . . <maxUEReport> >UE ID M BIT STRING ID of the UE (SIZE(16)) served by the cell in eNB₂. >CSI Report per CSI 1 . . . Process <maxCSIProcess> >> UE-CSI process M FFS FFS CSI process Configuration index configuration information. >> Reference type per 1 . . . CSI process <maxReferenceTypes> >>>Reference Type M ENUMERATED >>>RI M INTEGER (1 . . . Defined in TS 8, . . . ) 36.213 [11]. >>>Wideband CQI M 9.2.bb >>>Subband CQI List 0 . . . <maxSubband> >>>>Subband CQI O 9.2.cc If this IE is not present, the CQI is identical to the one provided for the last preceding subband. This IE is always present for the first subband in the list. >>>>Subband Start O INTEGER Corresponds to (2 . . . 109, . . . ) the PRB number of the first PRB in a subband defined in TS 36.213 [11] for the system bandwidth. If this IE is not present, the subband is contiguous with the previous subband in the list, or starts with PRB 0 if this is the first subband in the list. >>>>Subband Size O ENUMERATED Corresponds to a (2, 3, 4, 6, value of subband 8, . . . ) size k defined in TS 36.213 [11] for the system bandwidth. Ignored for the highest frequency subband. If this IE is not present, the size is identical to the one provided for the last preceding subband. This IE is always present for the first subband in the list.

Embodiment H H1. Introduction

In RAN3#88, after fruitful discussions on the exchange of CSI, a subband indexing scheme has been selected in the baseline CR (change request) [4]. In this document we identify some corrections that can be made and present them in a proposal.

H2. Discussion

A desirable feature that should be supported by a CSI signaling scheme is the exchange of both periodic and aperiodic CSI reports in the same X2 message. In the absence of this feature, i.e., when the sending eNB is forced to choose either the periodic or the aperiodic CSI report obtained under a CSI process of some user, the sending eNB will have to drop available CSI reports. This would be unfortunate given that precious over-the-air signaling resources have already been spent in acquiring these reports and that these reports can together convey more CSI that either individual one.

Accepting this view an indexing scheme to enable this feature has been selected in [4].

We identify two corrections and an improvement that can be made to the selected scheme:

Correction: Changing the subband index range to (0, . . . 27, . . . } from {0, . . . , 13, . . . }:

A benefit that can be obtained from the subband indexing scheme of [4] is the simple forwarding of both aperiodic and periodic CSI reports in the same X2 message. Notice that the maxSubband value is 14 and the subband index range is defined to be {0, . . . , 13, . . . }. This choice allows for simple forwarding with any configured periodic mode and when the configured a-periodic mode is 3-*. This is because in these cases the maximum number of subband reports is 14 and the index range spans {0, . . . , 13}, consistent with the agreed choice.

However, this choice will not allow the same X2 message to include aperiodic CSI report configured with feedback mode 2-* and periodic CSI report configured under any mode. This is because under aperiodic mode 2-*, when the total number of PRBs in the downlink is N_(RB) ^(DL)=110, the subband size is k=4 and the number of UE selected subbands is M=6 (Table 7.2.1.5 in TS36.213). Thus, we have N=28 subbands (110=4*27+2) and the UE is free to select any 6 out of these 28 subbands as its preferred ones. Consequently, the subband index identifying each UE selected subband must belong to the set {0, . . . , 27}.

Consequently, one of the two CSI process items should have a subband index range of {0, . . . , 27}. For simplicity we suggest a common subband index range of {0, . . . , 27} for both CSI process items. A slightly more efficient alternative could be where one of the two CSI process items (say CSI process item 1) has index range {0, . . . , 27} whereas the other one has index range {0, . . . , 13}.

2) Correction: Changing the semantic description to reflect that a different RI and CQI combination can be reported for each one of the two CSI process items under the same CSI process.

3) Improvement: Making the subband CQI IE optional with a clarification in the semantic description.

The subband CQIs are conveyed sequentially in the increasing order of subband indices. Then, in case the subband CQI IE for a subband is not conveyed, the receiving eNB must use the CQI conveyed for the last preceding subband. The CQI for the first subband must always be included. This approach can significantly save overhead by avoiding redundancy. Note that when a UE is configured in the aperiodic mode 2-*, it selects and reports indices for M out of N subbands. However, only one CQI (per codeword) is reported by it for all the M selected subbands. Therefore, it is beneficial that redundancy is avoided in reporting such CQIs in the X2 message as well.

H3. Conclusion

We identified three improvements that can be made in the UE-CSI IE and present them in a proposal.

9.2.aa UE-CSI Report

This IE provides CSI reports of UEs served by the cell for which the information is provided.

TABLE H1 IE type and Semantics IE/Group Name Presence Range reference description CSI Report per Cell 1 . . . <maxUEReport> >UE ID M BIT STRING ID assigned by (SIZE(16)) eNB2 for the UE. >CSI Report per CSI 1 . . . Process <maxCSIProcess> >>CSI Process M FFS Configuration Index >>CSI Report per 1 . . . CSI Process Item <maxCSIReport> >>>RI M INTEGER The RI (1 . . . 8, . . . ) corresponding to the CQI being reported for this CSI process Item. Value defined in TS 36.213 [11]. >>>Wideband CQI M 9.2.bb >>>Subband Size M ENUMERATED Corresponds to a (2, 3, 4, 6, value of subband 8, . . . ) size k defined in TS 36.213 [11]for the system bandwidth N_(RB) ^(DL) >>>Subband CQI 0 . . . List <maxSubband> >>>>Subband O 9.2.cc If this IE is not CQI present, the CQI is identical to the one provided for the last preceding subband. This IE is always present for the first subband in the list. >>>>Subband M INTEGER (0 . . . Index 27, . . . ) Range bound Explanation maxUEReport Maximum number of UE. Value is 128. maxCSIProcess Maximum number of CSI processes per UE. The value is 4. maxCSIReport Maximum number of CSI Reports per CSI Process. The value is 2. maxSubband Maximum number of subbands. The value is 14.

The foregoing is to be understood as being in every respect illustrative and exemplary, but not restrictive, and the scope of the invention disclosed herein is not to be determined from the Detailed Description, but rather from the claims as interpreted according to the full breadth permitted by the patent laws. It is to be understood that the embodiments shown and described herein are only illustrative of the principles of the present invention and that those skilled in the art may implement various modifications without departing from the scope and spirit of the invention. Those skilled in the art could implement various other feature combinations without departing from the scope and spirit of the invention. 

What is claimed is:
 1. In a wireless communications system including a first base station and a second base station, a wireless communications method implemented in the first base station supporting coordinated multi-point transmission and reception (CoMP), the wireless communications method comprising: receiving from the second base station an information element (IE) indicating multiple relative narrowband Tx (transmit) power (RNTP) thresholds; and performing interference aware scheduling.
 2. In a wireless communications system including a first base station and a second base station, a wireless communications method implemented in the second base station supporting coordinated multi-point transmission and reception (CoMP), the wireless communications method comprising: transmitting to the first base station an information element (IE) indicating multiple relative narrowband Tx (transmit) power (RNTP) thresholds, wherein the first base station performs interference aware scheduling.
 3. The wireless communications method as in claim 2, further comprising: deciding the multiple RNTP thresholds.
 4. The wireless communications method as in claim 2, wherein the IE includes a bitmap each position in which represents a physical resource block (PRB) in a subframe and indicates how transmission power in the PRB is mapped relative to the multiple thresholds.
 5. The wireless communications method as in claim 4, wherein a value in said each position is conveyed in 2 bits.
 6. The wireless communications method as in claim 5, wherein “00” indicates not exceeding a lowest threshold, and “11” indicates “no promise on the Tx power is given.”
 7. A first base station supporting coordinated multi-point transmission and reception (CoMP) and used in a wireless communications system, the first base station comprising: a receiver to receive from the second base station an information element (IE) indicating multiple relative narrowband Tx (transmit) power (RNTP) thresholds; and a controller to perform interference aware scheduling.
 8. The first base station as in claim 7, wherein the IE includes a bitmap each position in which represents a physical resource block (PRB) in a subframe and indicates how transmission power in the PRB is mapped relative to the multiple thresholds.
 9. The first base station as in claim 8, wherein a value in said each position is conveyed in 2 bits.
 10. The first base station as in claim 9, wherein “00” indicates not exceeding a lowest threshold, and “11” indicates “no promise on the Tx power is given.”
 11. A second base station supporting coordinated multi-point transmission and reception (CoMP) and used in a wireless communications system, the second base station comprising: a transmitter to transmit to the first base station an information element (IE) indicating multiple relative narrowband Tx (transmit) power (RNTP) thresholds, wherein the first base station performs interference aware scheduling.
 12. The second base station as in claim 11, further comprising: a controller to decide the multiple RNTP thresholds.
 13. The second base station as in claim 11, wherein the IE includes a bitmap each position in which represents a physical resource block (PRB) in a subframe and indicates how transmission power in the PRB is mapped relative to the multiple thresholds.
 14. The second base station as in claim 12, wherein a value in said each position is conveyed in 2 bits.
 15. The second base station as in claim 13, wherein “00” indicates not exceeding a lowest threshold, and “11” indicates “no promise on the Tx power is given.”
 16. A wireless communications method implemented in a wireless communications system supporting coordinated multi-point transmission and reception (CoMP) and including a first base station and a second base station, the wireless communications comprising: transmitting from the second base station to the first base station an information element (IE) indicating multiple relative narrowband Tx (transmit) power (RNTP) thresholds; and performing at the first base station interference aware scheduling.
 17. The wireless communications method as in claim 16, wherein the IE includes a bitmap each position in which represents a physical resource block (PRB) in a subframe and indicates how transmission power in the PRB is mapped relative to the multiple thresholds.
 18. The wireless communications method as in claim 17, wherein a value in said each position is conveyed in 2 bits.
 19. The wireless communications method as in claim 18, wherein “00” indicates not exceeding a lowest threshold, and “11” indicates “no promise on the Tx power is given.”
 20. A wireless communications system supporting coordinated multi-point transmission and reception (CoMP), the wireless communications system comprising: a first base station; and a second base station transmitting to the first base station an information element (IE) indicating multiple relative narrowband Tx (transmit) power (RNTP) thresholds, wherein the first base station performs interference aware scheduling. 